Title of Invention	PROCESS FOR PRODUCING AZETIDINONE COMPOUNDS
Abstract	The present invention relates to a method for producing an azetidinone compound represented by the following general formula [1], which comprises a step of reacting a compound represented by the following general formula [2] with a compound represented by the following general formula [3] in the presence of a base and a metal compound represented by the following general formula [4],

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Technical Field The present invention relates to a method for producing an azetidinone compound that is a key intermediate for synthesis of carbapenem type compounds. Background of the Invention (wherein R represents an alkyl group, a benzyl group that may have a substituent, or an aryl group that may have a substituent), which is a key intermediate for synthesis of an azetidinone compound having a p-methyl group at the V position of the 4-position-side chain usable for producing a lp-methylcarbapenem derivative which is important as an antibacterial agent, include a production method represented by the following reaction scheme 1: However, all these production methods have the following disadvantages respectively, thereby it cannot be said that they are fully satisfactory. Thus, the methods of the reaction schemes 1 to 3 use expensive starting materials and comprise many steps to need complicated operations, thereby being undesirable in terms not only of yield but also of costs. Further, the method of the reaction scheme 4 comprises relatively fewer steps for the production, however, the method inevitably uses an unstable silyl enol ether, thereby it is hard to say that the method is industrially useful and economic. Disclosure of the Invention An object of the present invention is to solve the above-described problems of the conventional methods, thereby providing a method for selectively obtaining a desired intermediate having a methyl group at the l'-P-position for synthesis of a carbapenem-type antibacterial agent under a mild condition in high yield by a simple process. The invention relates to a method for producing a compound represented by the following general formula [1]: 1 0 "X wherein R1, Rz, R\ and X are as defined below, characterized in that a compound represented by the following general formula [2]: wherein R1 represents a hydrogen atom or a hydroxy-protecting group, and L represents a leaving group, is reacted with a compound represented by the following general formula [3]: wherein R represents a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, R3 represents an alkyl group having 1 to 12 carbon atoms, a phenyl group which may have a substituent, an aralkyl group having 7 to 15 carbon atoms which may have a substituent, or a 5- to 8-membered alicyclic group which may have a substituent, and X represents an oxygen atom or a sulfur atom, in the presence of a base and a metal compound represented by the following general formula [4]: MYn(R4)m [4] wherein M represents a metal atom, Y represents a halogen atom, R4 represents a lower alkyl group having 1 to 4 carbon atoms, a lower alkoxy group having 1 to 4 carbon atoms, a phenoxy group which may have a substituent, an alkylsulfonyldioxy group, an arylsulfonyldioxy group, an alkylsulfonyloxy group, an arylsulfonyloxy group, a cyclopentadienyl group, or a pentamethylcyclopentadienyl group, and n and m represent an integer of 0 to 4, the sum of n and m being the atomic valence of M. Thus, as a result of intense research in view of the above object, the inventors have found that a desired azetidinone compound [1] having a l'-p-configuration can be selectively produced in high yield only by reacting a compound represented by the general formula [2] and a diazo compound represented by the general formula [3] in the > presence of a particular metal compound and a base, and thereby the invention has been accomplished. The invention provides a method for selectively producing a desired azetidinone compound having a l'-p-configuration under a mild condition in high yield by a simple process of only reacting the compound represented by the general formula [2] with the diazo compound represented by the general formula [3] in the presence of the particular metal compound and the base without converting the diazo compound into a silyl enol ether. Best Mode for Carrying Out the Invention In the compound represented by the general formula [2] used in the production method of the present invention, the hydroxy-protecting group represented by R1 may be any hydroxy-protecting group that is generally used in the fields of peptide chemistry or P-lactam compounds, etc. Thus, examples of the hydroxy-protecting groups include tri-substituted silyl groups including tri(Cl-6 alkyl)silyl groups such as a trimethylsilyl group, a triethylsilyl group, a triisopropylsilyl group, a dimethylisopropylsilyl group, a diethylisopropylsilyl group, a dimethyl(2,3-dimethyl-2-butyl)silyl group, a tert-butyldimethylsilyl group, and a dimethylhexylsilyl group, di-(C 1 -6 alkyl)-(C6-18 aryl)silyl groups such as a dimethylcumylsilyl group, di-(C6-18 aryl)-(C 1 -6 alkyl)silyl groups such as a tert-butyldiphenylsilyl group and a diphenylmethylsilyl group, tri-(C6-18 aryl)silyl groups such as a triphenylsilyl group, and tri-(C7-19 aralkyl)silyl groups such as a tribenzylsilyl group and a tri-p-xylylsilyl group; aralkyl groups having 7 to 19 carbon atoms, in which 1 to 3 hydrogen atoms may be substituted by an alkoxy group having 1 to 4 carbon atoms (e.g. a methoxy group, an ethoxy group), a nitro group, etc., such as a benzyl group, a 4-methoxybenzyl group, a 2-nitrobenzyl group, a 4-nitrobenzyl group, a diphenylmethyl group, and a triphenylmethyl group; alkyloxycarbonyl groups having 1 to 6 carbon atoms, in which 1 to 3 hydrogen atoms may be substituted by an alkoxy group having 1 to 4 carbon atoms (e.g. a methoxy group, an ethoxy group), a halogen atom (e.g. fluorine, chlorine, bromine, iodine), a tri-(Cl-4 alkyl)silyl group (e.g. a trimethylsilyl group), etc., such as a methoxycarbonyl group, an ethoxycarbonyl group, a tert-butoxycarbonyl group, a 2,2,2-trichloroethoxycarbonyl group, and a 2-trimethylsilylethoxycarbonyl group; aralkyloxycarbonyl groups having 7 to 10 carbon atoms, in which 1 to 3 hydrogen atoms may be substituted by an alkoxy group having 1 to 4 carbon atoms (e.g. a methoxy group, an ethoxy group) or a nitro group, such as a benzyloxycarbonyl group, a 2-nitrobenzyloxycarbonyl group, a 4-nitrobenzyloxycarbonyl group, a 4-methoxybenzyloxycarbonyl group, and a 3,4-dimethoxybenzyloxycarbonyl group; alkenyloxycarbonyl groups having 2 to 6 carbon atoms such as a vinyloxycarbonyl group and an allyloxycarbonyl group; an acyl groups, in which 1 to 3 hydrogen atoms may be substituted by a halogen atom (e.g. fluorine, chlorine, bromine, iodine), a nitro group, etc., such as a formyl group, an acetyl group, a chloroacetyl group, a dichloroacetyl group, a trichloroacetyl group, a trifluoroacetyl group, a propionyl group, a butyryl group, a benzoyl group, a 4-toluoyl group, a 4-anisoyl group, and a 4-nitrobenzoyl group; cyclic protecting groups such as a tetrahydropyranyl group and a tetrahydrofuranyl group; etc. Preferred protecting groups among them include aralkyloxycarbonyl groups having 7 to 19 carbon atoms such as a benzyloxycarbonyl group and a 4-nitrobenzyloxycarbonyl group, alkenyloxycarbonyl groups having 2 to 6 carbon atoms such as an allyloxycarbonyl group, tri-(Cl-6 alkyl)silyl groups, etc., and more preferred ones include a tert-butyldimethylsilyl group, etc. Examples of the leaving groups represented by L include acyloxy groups (e.g. alkanoyloxy groups, aroyloxy groups, arylalkanoyloxy groups, alkylsulfonyloxy groups, arylsulfonyloxy groups, alkoxycarbonyloxy groups, aralkoxycarbonyloxy groups, alkoxyalkanoyloxy groups, carbamoyloxy groups, etc.), alkanoylthio groups, aroylthio groups, alkylthio groups, arylthio groups, alkylsulfinyl groups, arylsulfinyl groups, alkylsulfonyl groups, arylsulfonyl groups, halogen atoms, etc. In the case where L is an alkanoyloxy group, specific examples thereof include normal alkanoyloxy groups, which may have 1 to 3 substituents of a halogen atom, a cyano group, etc., such as an acetoxy group, a propionyloxy group, a butyryloxy group, an a-fluoroacetoxy group, an ct-chloroacetoxy group, an a-bromoacetoxy group, an ot-iodoacetoxy group, an ot,a-difluoroacetoxy group, an a,ot-dichloroacetoxy group, and an oc-cyanoacetoxy group; branched or cyclic alkanoyloxy groups such as an isobutyryloxy group and a cyclohexylcarbonyloxy group; etc. In the case where L is an aroyloxy group, specific examples thereof include monocyclic or polycyclic aroyloxy groups, which may have a heteroatom, such as a benzoyloxy group, a 1-naphthoyloxy group, a 2-naphthoyloxy group, a nicotinoyloxy group, an isonicotinoyloxy group, and a furfuroyloxy group. In the case where L is an arylalkanoyloxy group, specific examples thereof include a phenylacetoxy group, etc. In the case where L is an alkylsulfonyloxy group, specific examples thereof include a methanesulfonyloxy group, an ethanesulfonyloxy group, a propanesulfonyloxy group, a trifluoromethanesulfonyloxy group, etc. In the case where L is an arylsulfonyloxy group, specific examples thereof include a benzenesulfonyloxy group, a p-toluenesulfonyloxy group, etc. In the case where L is an alkoxycarbonyloxy group, specific examples thereof include a methoxycarbonyloxy group, an ethoxycarbonyloxy group, etc. In the case where L is an aralkoxycarbonyloxy group, specific examples thereof include a benzyloxycarbonyloxy group, etc. In the case where L is an alkoxyalkanoyloxy group, specific examples thereof include a methoxyacetoxy group, an ethoxyacetoxy group, etc. In the case where L is a carbamoyloxy group, specific examples thereof include an N-methylcarbamoyloxy group, an N-ethylcarbamoyloxy group, an N-phenylcarbamoyloxy group, etc. In the case where L is an alkanoylthio group, specific examples thereof include an acetylthio group, a propionylthio group, etc. In the case where L is an aroylthio group, specific examples thereof include a benzoylthio group, a naphthoylthio group, etc. methylthio group, an ethylthio group, a n-propylthio group, an isopropylthio group, a n-butylthio group, an isobutylthio group, a tert-butylthio group, etc. In the case where L is an arylthio group, specific examples thereof include a phenylthio group, a naphthylthio group, etc. In the case where L is an alkylsulfinyl group, specific examples thereof include a methanesulfinyl group, an ethanesulfinyl group, a n-propanesulfinyl group, a n-butanesulfinyl group, etc. In the case where L is an arylsulfinyl group, specific examples thereof include a benzenesulfinyl group, a p-toluenesulfinyl group, etc. In the case where L is an alkylsulfonyl group, specific examples thereof include a methanesulfonyl group, an ethanesulfonyl group, a n-propanesulfonyl group, a n-butanesulfonyl group, etc. In the case where L is an arylsulfonyl group, specific examples thereof include a benzenesulfonyl group, a p-toluenesulfonyl group, etc. In the case where L is a halogen atom, specific examples thereof include fluorine, chlorine, bromine, iodine, etc. Particularly preferred leaving groups among them include an acetoxy group, etc. In the compound represented by the general formula [3] used in the production method of the invention, specific examples of the lower alkyl groups having 1 to 4 carbon atoms represented by R include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, etc. Preferred R include a hydrogen atom and a methyl group. In the general formula [3], specific examples of the alkyl groups having 1 to 12 carbon atoms represented by R include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, etc. Specific examples of the alkenyl groups having 2 to 5 carbon atoms represented by R include a vinyl group, an allyl group, a 1 -propenyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, a 2-methylallyl group, etc. In the phenyl group represented by R which may have a substituent, examples of the substituents include lower alkyl groups having 1 to 4 carbon atoms, lower alkoxy groups having 1 to 4 carbon atoms, a nitro group, halogen atoms, etc. Specific examples of the lower alkyl groups having 1 to 4 carbon atoms of the substituent include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, etc. Further, specific examples of the lower alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, etc. Furthermore, specific examples of the halogen atoms include fluorine, chlorine, bromine, iodine, etc. In the aralkyl group having 7 to 15 carbon atoms represented by R which may have a substituent, examples of the substituents include lower alkyl groups having 1 to 4 carbon atoms, lower alkoxy groups having 1 to 4 carbon atoms, a nitro group, halogen atoms, etc. Specific examples of the lower alkyl groups having 1 to 4 carbon atoms of the substituent include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, etc. Further, specific examples of the lower alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, etc. Furthermore, specific examples of the halogen atoms include fluorine, chlorine, bromine, iodine, etc. Specific examples of the aralkyl groups having 7 to 15 carbon atoms which may have a substituent include a benzyl group, an ot-phenethyl group, a (5-phenethyl group, an oc-phenylpropyl group, a p-phenylpropyl group, a y-phenylpropyl group, a naphthyl methyl group, etc. Specific examples of the 5- to 8-membered alicyclic groups represented by R , which may have a substituent, include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, etc. Examples of the substituents include lower alkyl groups having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, etc. Examples of particularly preferred R among them include lower alkyl groups having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and a tert-butyl group; aralkyl groups having 7 to 15 carbon atoms, which may have a substituent (e.g. a nitro group and a methoxy group) such as a benzyl group, a p-nitrobenzyl group, and a p-methoxybenzyl group; alkenyl groups having 2 to 5 carbon atoms such as a vinyl group and an allyl group. In the metal compound represented by the general formula [4] used in the production method of the invention, the metal atoms represented by M include metal atoms ordinarily used in organic synthetic chemistry including carbon-carbon bond formation reactions, etc., and more specific examples thereof include metals of Group 4 of the Periodic Table of Elements adopted by IUPAC such as titanium and zirconium; metals of Group 14 of the Periodic Table of Elements adopted by IUPAC such as silicon and tin; metals of Group 13 of the Periodic Table of Elements adopted by IUPAC such as boron and aluminum; metals of Group 3 of the Periodic Table of Elements such as scandium, yttrium, and lanthanoid (lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, erbium, ytterbium, etc.); metals of Group 8 of the Periodic Table of Elements such as iron and ruthenium; metals of Group 12 of the Periodic Table of Elements such as zinc; etc. In the general formula [4], examples of the halogen atoms represented by Y include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. In the general formula [4], specific examples of the lower alkyl groups having 1 to 4 carbon atoms represented by R4 include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, etc., and specific examples of the lower alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, etc. In the phenoxy group represented by R which may have a substituent, examples of the substituents include lower alkyl groups having 1 to 4 carbon atoms, lower alkoxy groups having 1 to 4 carbon atoms, halogen atoms, etc. Specific examples of the lower alkyl groups having 1 to 4 carbon atoms of the substituent include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, etc., specific examples of the lower alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, etc., and specific examples of the halogen atoms include fluorine, chlorine, bromine, iodine, etc. Specific examples of the alkylsulfonyldioxy groups represented by R4 include a methanesulfonyldioxy group, an ethanesulfonyldioxy group, a trifluoromethanesulfonyldioxy group, etc. Specific examples of the arylsulfonyldioxy groups represented by R4 include a benzenesulfonyldioxy group, a p-toluenesulfonyldioxy group, etc. Specific examples of the alkylsulfonyloxy groups represented by R4 include a methanesulfonyloxy group, an ethanesulfonyloxy group, a trifluoromethanesulfonyloxy group, etc. Specific examples of the arylsulfonyloxy group represented by R4 include a benzenesulfonyloxy group, a p-toluenesulfonyloxy group, etc. The compound represented by the general formula [2] may be synthesized by a method described in J. Am. Chem. Soc9 Vol. 112, pp. 7820 to 7822 (1990), Tetrahedron Letters, Vol. 32, pp. 2145 to 2148 (1991), Tetrahedron Letters, Vol. 32, pp. 5991 to 5994 (1991), etc., or a method based thereon, etc., though the synthesis method is not particularly restricted to these methods. More preferred ones among these compounds include 4-acetoxy-3-[l-tert-butyldimethylsilyloxyethyl]-azetidin-2-one, 4-a-chloroacetoxy-3-[l-tert-butyldimethylsilyloxyethyl]-azetidin«2-one? etc. The diazo compound represented by the general formula [3] may be synthesized by a method described in JP-A-58-103358 or JP-A-61-275284, or a method based thereon, etc., though the synthesis method is not particularly restricted to the methods. Specific examples of the diazo compounds represented by the general formula [3] include methyl 2-diazo-3-oxobutanoate, methyl 2-diazo-3-oxopentanoate, methyl 2-diazo-3-oxohexanoate, ethyl 2-diazo-3-oxobutanoate, ethyl 2-diazo-3-oxopentanoate, ethyl 2-diazo-3-oxohexanoate, n-propyl 2-diazo-3-oxobutanoate, n-propyl 2-diazo-3-oxopentanoate, n-propyl 2-diazo-3-oxohexanoate, isopropyl 2-diazo-3-oxobutanoate, isopropyl 2-diazo-3-oxopentanoate, isopropyl 2-diazo-3-oxohexanoate, n-butyl 2-diazo-3-oxobutanoate, n-butyl 2-diazo-3-oxopentanoate, n-butyl 2-diazo-3-oxohexanoate, tert-butyl 2-diazo-3 -oxobutanoate, tert-butyl 2-diazo-3 -oxopentanoate, tert-butyl 2-diazo-3-oxohexanoate, benzyl 2-diazo-3-oxobutanoate, benzyl 2-diazo-3-oxopentanoate5 benzyl 2-diazo-3-oxohexanoate, p-nitrobenzyl 2-diazo-3-oxobutanoate, p-nitrobenzyl 2-diazo-3-oxopentanoate, p-nitrobenzyl 2-diazo-3-oxohexanoate, p-methoxybenzyl 2-diazo-3-oxobutanoate, p-methoxybenzyl 2-diazo-3-oxopentanoate, p-methoxybenzyl 2-diazo-3-oxohexanoate, vinyl 2-diazo-3-oxobutanoate, vinyl 2-diazo-3-oxopentanoate, vinyl 2-diazo-3-oxohexanoate, allyl 2-diazo-3-oxobutanoate, allyl 2-diazo-3-oxopentanoate, allyl 2-diazo-3-oxohexanoate, etc. More preferred ones among these azo compounds include tert-butyl 2-diazo-3-oxopentanoate, benzyl 2-diazo-3-oxopentanoate, p-nitrobenzyl 2-diazo-3-oxopentanoate, allyl 2-diazo-3-oxopentanoate, etc. The metal compound represented by the general formula [4] used in the invention may be a commercially available one, which may be directly used or purified to use if necessary. Specific examples of the metal compounds represented by the general formula [4] include titanium compounds such as TiCU, TiCl3(OCH3), TiCl3(OC2H5), TiCl3(0-n-Pr), TiCl3(0-i-Pr), TiCl3(OBu)? TiCl3(0-i-Bu), TiCl3(0-sec-Bu), TiCl3(0-tert-Bu)? TiCl2(OMe)2, TiCl2(OEt)2, TiCl2(0-n-Pr)2, TiCl2(0-i-Pr)2, TiCl2(OBu)2, TiCl2(0-i-Bu)2, TiCl2(0-sec-Bu)2, TiCl2(0-tert-Bu)2, Ti(Cp)2Cl2, Ti(Cp )2C12, TiBr4, and TiLt; zinc compounds such as ZnCl2, ZnBr2, and Znl2; zirconium compounds such as ZrCl4, ZrCl3(OMe), ZrCl3(OEt), ZrCl3(0-n-Pr), ZrCl3(0-i-Pr), ZrCl3(0-n-Bu), ZrCl3(0-i-Bu), ZrCl3(0-sec-Bu)5 ZrCl3(0-tert-Bu), Zr(Cp)2Cl2, Zr(Cp,)2Cl2, ZrBr4, and ZrU; aluminum compounds such as A1C13, Al(OMe)3, Al(OEt)3? Al(0-n-Pr)3, Al(0-i-Pr)3, AlCl2Me, AlClMe2, AlMe3, AlCl2Et, AlClEt2, AlEt3? AlBr3, and AII3; tin compounds such as SnCU, SnBr4, S11I4, and Sn(OS02CF3)2; iron compounds such as FeCl3, FeBr3, and Fel3; boron compounds such as (2Hs2O , BF3, (CH3)2BOS02CF3, (C2H5)2BOS02CF3, (Pr)2BOS02CF3, and (Bu)2BOS02CF3; silicon compounds such as (CH3)3SiOS02CF3 and (CH3)3SiCl; scandium compounds such as ScF3, ScCl3, ScBr3, SCI3, Sc(Oi-Pr)3, and Sc(OS02CH3)3; yttrium compounds such as YF3, YCI3, YBr3, YI3, Y(0-i-Pr)3, and Y(OS02CH3)3; lanthanum compounds such as LaF3, LaCU, LaBr3, Lal3, La(Oi-Pr)3, and La(OS02CH3)3; cerium compounds such as CeF3, CeCl3, CeBr3, Cel3, Ce(0-i-Pr)3, and Ce(OS02CH3)3; praseodymium compounds such as PrF3, PrCU, PrBr3, Prl3, Pr(0-i-Pr)3, and Pr(OS02CH3)3; neodymium compounds such as NdF3? NdCl3, NdBr3? Ndl3, Nd(0-i-Pr)3, and Nd(OS02CH3)3; samarium compounds such as S111F3, SmCU, SmBr3, Sml3, Sm(Oi-Pr)3, and Sm(OS02CH3)3; gadolinium compounds such as GdF3, GdCl3, GdBr3, Gdl3, Gd(Oi-Pr)3? and Gd(OS02CH3)3; dysprosium compounds such as DyF3, DyCb, DyBr3, Dyl3? Dy(0-i-Pr)3, and Dy(OS02CH3)3; erbium compounds such as ErF3? ErCl3, ErBr3, Erl3, Er(0-i-Pr)3, and Er(OS02CH3)3; ytterbium compounds such as YbF3, YbCl3, YbBr3, YW3, Yb(0-i-Pr)3? and Yb(OS02CH3)3; etc. In the above examples, Cp represents a cyclopentadienyl group, and Cp represents a pentamethylcyclopentadienyl group. More preferred metal compounds among them include HCI4 (titanium tetrachloride), ZnCl2 (zinc dichloride), ZrCU (zirconium tetrachloride), AICI3 (aluminum trichloride), SnCU (tin tetrachloride), (C2Hs)20 • BF3 (boron trifluoride etherate), (CH3)3SiOS02CF3 (trimethylsilyl triflate), (CH3)3SiCl (trimethylsilyl chloride), etc. These metal compounds may be used singly or in combination of 2 or more compounds. Examples of the bases used in the production method of the invention include primary amines, secondary amines, tertiary amines, pyridines, etc. In the case where the base is a primary amine, specific examples thereof include ethylamine, propylamine, butylamine, aniline, benzylamine, etc. In the case where the base is a secondary amine, specific examples thereof include diethylamine, di-n-propylamine, diisopropylamine, methylisopropylamine, ethylisopropylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, N-methylaniline, N-ethylaniline, pyrrolidine, piperidine, morpholine, piperazine, imidazole, dibenzylamine, etc. In the case where the base is a tertiary amine, specific examples thereof include trimethylamine, triethylamine, tripropylamine, triisopropylamine, diisopropylmethylamine, diisopropylethylamine, tri-n-butylamine, tribenzylamine, N-methylpiperidine, N-ethylpiperidine, N-methylmorpholine, N-ethylmorpholine, l,5-diazabicyclo[4.3.0]-5-nonene, l,8-diazabicyclo[5.4.0]-7-undecene, 1,4-diazabicyclo [2.2.2]octane, N,N,N,N-tetramethylethylenediamine, N,N,N,N-tetramethyl-l,3-propanediamine, dimethylaniline, diethylaniline, etc. In the case where the base is a pyridines, specific examples thereof include pyridine, a-picoline, (5-picoline, y-picoline, 2,6-lutidine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, N,N-dimethylaminopyridine, quinoline, isoquinoline, etc. Among these bases, triethylamine, tri-n-butylamine, diisopropylethylamine, N-methylpiperidine, N-ethylpiperidine, N-methylmorpholine, N-ethylmorpholine, l,5-diazabicyclo[4.3.0]-5-nonene, l,8-diazabicyclo[5.4.0]-7-undecene, 1,4-diazabicyclo [2.2.2]octane, N,N-dimethylaminopyridine, etc. are more preferable because they are versatile and provide high reaction selectivity and yield. These bases may be used singly or as a combination of 2 or more bases. The base used in the invention may be a commercially available one, which may be used directly or purified if necessary. The production method of the invention is desirably carried out in an organic solvent under an atmosphere of an inert gas such as argon and nitrogen. The azetidinone compound represented by the general formula [1] may be produced by reacting the diazo compound represented by the general formula [3] and the metal compound represented by the general formula [4] with the base, and then reacting with the compound represented by the general formula [2], under such conditions. The organic solvent for the reaction may be any inert solvent that does not take part in the reaction, and examples thereof include hydrocarbon-based solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon-based solvents such as cyclohexane and methylcyclohexane; halogenated hydrocarbon-based solvents such as dichloromethane, dichloroethane, chloroform, and dibromoethane; aromatic hydrocarbon-based solvents such as benzene, chlorobenzene, toluene, and xylene; ether-based solvents such as diethyl ether, diisopropyl ether, tetrahydrofuran, dimethoxyethane, 1,3-dioxolane, and 1,4-dioxane; nitrile-based solvents such as acetonitrile and propionitrile; amide-based solvents such as dimethylformamide and dimethylacetamide; etc. These solvents may be used singly or as a mixed solvent of 2 or more solvents. More preferred solvents among them include the halogenated hydrocarbon-based solvents, the aromatic hydrocarbon-based solvents, the ether-based solvents, etc., and furthermore preferred are dichloromethane, toluene, xylene, tetrahydrofuran, etc., which are versatile and provide high reaction selectivity and yield. The amount of these solvents used is generally about 1- to 50-fold by volume, preferably about 5- to 20-fold by volume, of the compound represented by the general formula [2], though there are no particular restrictions thereon. The reaction temperature is generally about -70 to 100°C, preferably about -70 to 0°C, and the reaction can be smoothly carried out by keeping the temperature for approximately 5 minutes to 5 hours, preferably approximately 10 minutes to 3 hours. In the invention, the amount of the diazo compound represented by the general formula [3] used is about 0.5- to 5-fold mol, preferably about 0.7- to 4-fold mol, per 1 mol of the compound represented by the general formula [2], In the invention, the amount of the metal compound represented by the general formula [4] used is about 0.5- to 2.5-fold mol, preferably about 0.7- to 2-fold mol, per 1 mol of the compound represented by the general formula [2]. In the invention, the amount of the base used is about 1- to 8-fold mol, preferably about 1.4- to 4-fold mol, per 1 mol of the compound represented by the general formula [2]. In the above reaction, the desired p-isomer-content is generally about 85% or more in the case where R is an alkyl group such as a methyl group, though the ratio of the produced a-isomer and P-isomer is slightly changed depending on the type of the diazo compound represented by the general formula [3], the type of the metal compound represented by the general formula [4], or the various reaction conditions. The desired azetidinone compound can be obtained from the above reaction mixture by an aftertreatment method known per se such as solvent extraction, redissolution, crystallization, recrystallization, and various chromatographies. The azetidinone compound represented by the general formula [1], obtained by the production method of the invention, can be easily converted to carbapenem compounds represented by the general formula [B]: 1 2 wherein R represents an acyl group and R has the same meaning as above, by using a known production method. Examples The present invention will be explained in more detail referring to Examples below, however it is not limited to these Examples. Example 1. Production of (3S,4R)-3-[(R)-l-tert-butyldimethylsilyloxyethyl]-4- [(R)-l-methyl-3-diazo-3-p-nitrobenzyloxycarbonyl-2-oxo-propyl]-azetidin-2-one Under a nitrogen atmosphere, 15 mL of a methylene chloride solution containing 2.22 g (8.0 mmol) of p-nitrobenzyl 2-diazo-3-oxobutanoate was cooled to -40°C, 0.39 mL (3.55 mmol) of titanium tetrachloride was added to and stirred at -40°C for 30 minutes, and 1.81 mL (7.57 mmol) of tributylamine was added and further stirred at -40°C for 30 minutes. Then, to this reaction mixture was added 5 mL of a methylene chloride solution containing 574 mg (2.0 mmol) of (3R,4R)-4-acetoxy-3-[(R)-1 -tert-butyldimethylsilyloxyethyl] -azetidin-2-one dropwise, and the reaction mixture was further stirred at -40°C for 1 hour. The reaction mixture was poured into a 10% aqueous sodium hydrogen carbonate solution to stop the reaction, and the organic layer was separated and washed with water. As a result of analyzing the organic layer by a high performance liquid chromatography, the ratio P:a was 95:5. The obtained organic layer was dried over anhydrous magnesium sulfate, the solvent was distilled off, and the residue was purified by a column chromatography, to obtain 757 mg of the [3-methyl isomer of the subject compound (75% yield). The physical properties of this compound corresponded with those described in JP-A-61-275284. Example 2. Production of (3S,4R)-3-[(R)-l-tert-butyldimethylsilyloxyethyl] -4-[(R)-l-methyl-3-diazo-3-p«nitrobenzyloxycarbonyl-2-oxo-propyl]-azetidin-2-one Under a nitrogen atmosphere, 20 mL of a methylene chloride solution containing 1.66 g (6.0 mmol) of p-nitrobenzyl 2-diazo-3-oxobutanoate was cooled to -40°C, 0.66 mL (6.0 mmol) of titanium tetrachloride was added to and stirred at -40°C for 30 minutes, and 1.65 mL (12.0 mmol) of n-ethylpiperidine was added to and further stirred at -40°C for 30 minutes. Then, to this reaction mixture was added 5 mL of a methylene chloride solution containing 1.72 g (6.0 mmol) of (3R,4R)-4-acetoxy« 3-[(R)-l-tert-butyldimethylsilyloxyethyl]-azetidin-2-one dropwise, and the mixture was further stirred at -40°C for 1 hour. 10 mL of 1 molar hydrochloric acid was added to the reaction mixture to stop the reaction, and the organic layer was separated and washed with water. As a result of analyzing the organic layer by a high performance liquid chromatography, the ratio P:a was 98:2. The obtained organic layer was dried over anhydrous magnesium sulfate, the solvent was distilled off, and the residue was purified by a column chromatography, to obtain 2.09 g of the (3-methyl isomer of the subject compound (69% yield). Examples 3 and 4 The reaction and the aftertreatments were carried out in the same manner as Example 1 except for using each of the metal compounds shown in following Table 1 instead of titanium tetrachloride, thereby the azetidinone compounds equal to Example 1 were obtained in the following yield at the following production rate, respectively. The results are shown in Table 1 together. Example 5 The reaction and the aftertreatments were carried out in the same manner as Example 1 except for using titanium tetrachloride and trimethylsilyl chloride as metal compounds, thereby the azetidinone compound equal to Example 1 was obtained in 68% yield at the production rate P-isomer:oc-isomer of 95:5. Example 6 The reaction and the aftertreatments were carried out in the same manner as Example 1 except that the reaction temperature was changed from -40°C to 5°C and triethylamine was used as a base instead of tributylamine, thereby the azetidinone compound equal to Example 1 was obtained in 69% yield at the production rate P-isomer:a-isomer of 95:5. Comparative Example 1 The reaction was carried out in the same manner as Example 1 except for using no bases, and as a result, the target compound was not obtained at all. Examples 7 to 9 The reaction and the aftertreatments were carried out in the same manner as Example 1 except for using each of the reaction solvents shown in following Table 2 instead of methylene chloride, thereby the azetidinone compounds equal to Example 1 were obtained in the following yield at the following production rate, respectively. The results are shown in Table 2 together. Examples 10 to 13 The reaction and the aftertreatments were carried out in the same manner as Example 1 except for using each of the compounds, which were such that the p-nitrobenzyl group of p-nitrobenzyl 2-diazo-3-oxobutanoate (the compound with R being the p-nitrobenzyl group in the above chemical formula) was replaced by each of the substituents shown in following Table 3, as an azo compound, thereby the P-methyl isomers were obtained with high selectivity for various azetidinone compounds, respectively. The results are shown in Table 3 together. l-2-oxo-propyl]-azetidin-2-one was dissolved in 750 mL of methanol, and then 44.5 mL of a 2 molar hydrochloric acid aqueous solution was added to and stirred at the room temperature for 22.5 hours. 1.1 L of ethyl acetate was added and stirred, and then the organic layer was separated and washed with water. The obtained organic layer was dried over anhydrous magnesium sulfate, and the solvent was distilled off to obtain 107.6 g of a desilylated product. 107.6 g of the obtained desilylated product was dissolved in 1.1 L of ethyl acetate, and 0.65 g of rhodium octanoate (Rli2(Oct)4) was added and reacted at 50°C for 2.5 hours. The solvent was distilled off, the resultant residue was dissolved in 550 mL of acetonitrile and cooled to -10°C, and then 77.8 g of diphenyl chlorophosphate and 39.2 g of diisopropylethylamine were added in this order and stirred at -10°C for 3 hours. The solvent was distilled off and the residue was dissolved in 2.2 L of ethyl acetate. Thus-obtained organic layer was washed with water, the solvent was distilled off, and heptane was added to the resultant to form crystals. The crystals were separated by filtration and dried to obtain 137.9 g of the subject compound. The physical properties of this compound corresponded with those described in Heterocycles, Vol. 21, pp. 29-40 (1984) and JP-A-6-321946. Industrial Applicability The present invention has a remarkable effect in providing a method for producing an azetidinone compound under a mild condition with high yield and selectivity by a simple process, wherein the azetidinone compound is a key synthetic intermediate for industrially manufacturing lp-methylcarbapenem derivatives, which are suitably used for production of carbapenem type antibiotics useful as antibacterial agents. WE CLAIM: 1. A method for producing an azetidinone compound represented by the following general formula [1], which comprises a step of reacting a compound represented by the following general formula [2] with a compound represented by the following general formula [3] in the presence of a base and a metal compound represented by the following general formula [4], wherein said general formula[l] is: (wherein R,R,R, and X are as defined below), said general formula [2] is: (wherein R1 represents a hydrogen atom or a hydroxyprotecting group, and L represents a leaving group}, said general formula [3] is : (wherein R represents a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, R3 represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, a phenyl group which may have a substituent, an aralkyl -28- group having 7 to 15 carbon atoms which may have a substituent, or a 5- to 8-membered alicyclic group which may have a substituent, and X represents an oxygen atom or a sulfur atom), (wherein M represents a metal atom, Y represents a halogen atom, R4 represents a lower alkyl group having 1 to 4 carbon atoms, a lower alkoxy group having 1 to 4 carbon atoms, a phenoxy group which may have a substituent, an alkylsulfonyldioxy group, an arylsulfonyldioxy group, an alkylsulfonyloxy group, an arylsulfonyloxy group, a cyclopentadienyl group, or a pentamethylcyclopentadienyl group, and n and m represent an integer of 0 to 4, the sum of n and m being the atomic valence of M). 2. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 4 of the Periodic table of elements. 3. The method as claimed in claim 2, wherein the metal atom of Group 4 of the Periodic table of elements is titanium or zirconium. 4. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 14 of the Periodic table of elements. 5. The method as claimed in claim 4, wherein the metal atom of Group 14 of the Periodic table of elements is silicon or tin. 6. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 13 of the Periodic table of elements. 7. The method as claimed in claim 6, wherein the metal atom of Group 13 of the Periodic table of elements is boron or aluminum. 8. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 3 of the Periodic table of elements. 9. The method as claimed in claim 8, wherein the metal atom of Group 3 of the Periodic table of elements is scandium, yttrium, or a lanthanoid. 10. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 8 of the Periodic table of elements. 11. The method as claimed in claim 10, wherein the metal atom of Group 8 of the Periodic table of elements is iron or ruthenium. 12. The method as claimed in claim 1, wherein the metal atom represented by M in the general formula [4] is a metal atom of Group 12 of the Periodic table of elements. 13. The method as claimed in claim 12, wherein the metal atom of Group 12 of the Periodic table of elements is zinc. 14. The method as claimed in any one of claims 1 to 13, wherein the base is a primary amine, a secondary amine, a tertiary amine, and/or pyridines. 15. A method for producing a compound of formula (1) substantially as herein described and exemplified.

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