Patent GB-1322471-A (GB)
Title: Process for preparing cephem-4-carboxylic acid esters
IPC: C07F9/54
Filed: 1971-12-23
Abstract: 1322471 Preparing 3-methyl-cephalosporanic acid esters FARBWERKE HOECHST AG 23 Dec 1971 [28 Dec 1970] 60064/71 Headings C2A C2C and C2P 3-Methyl-cephalosporanic acid esters having the general Formula (1): wherein R is an acyl radical and R<SP>1</SP> is an optionally substituted alkyl, cycloalkyl or aryl radical are prepared by heating a penicillin sulphoxide ester of Formula (2): wherein R and R<SP>1</SP> have the aforesaid meanings, in the presence of a phosphonium salt of Formula (3): in which R<SP>1</SP>, R<SP>2</SP> and R<SP>3</SP> may be the same or different and each is an unsubstituted or substituted hydrocarbon radical, R<SP>4</SP> is a methyl group substituted by an electrophilic radical and optionally a further substituent, and X- is an organic or inorganic anion. The acyl radical R may be a natural or semisynthetic penicillin 6-acylating group, and if it contains groups (e.g. amino or carboxyl) which are labile under the reaction conditions of the process, these groups are first protected, e.g. by carbobenzoxylation or esterification. R<SP>1</SP> is an ester-forming group which can subsequently be removed without affecting the structure of the cephem ring, such groups being benzyl, benzhydryl, trityl, p-nitro- or p-methoxybenzyl, 2,2,2-trichloroethyl, tert.-butyl, phenacyl, isobornyl and adamantyl groups. R<SP>1</SP>, R<SP>2</SP> and R<SP>3</SP> in the phosphonium compound are preferably n-butyl, n-octyl, phenyl, tolyl and benzyl radicals. The electrophilic substituent on R<SP>4</SP> may be cyano, alkoxy carbonyl, p-nitrophenyl or acyl. Preferred alkoxy carbonyl groups are ester groups of an alkanol having up to 8 carbons which may be substituted, e.g. by phenyl. The acyl group is preferably acetyl, acryloyl or an acyl group of a benzene acid which may be ring- substituted by Cl, Br, alkyl, alkoxy or nitro. The further substituent on R<SP>4</SP> is alkyl, aryl or an acylamido group of formula wherein A is alkyl which may be phenylsubstituted, B is aryl or the same as A, or A and B together represent an alkylene group of up to 11 carbons, optionally alkyl-substituted. X- may be the anion of amidosulphonic, sulphuric, or a phosphoric, phosphonic, sulphonic or hydrohalic acid. The preferred phosphonium salt is 1-azetidine-2 - ono - methoxycarbonylmethyl - triphenylphosphonium - p - toluenesulphonate. The reaction may be conducted at 80 to 195 C., preferably in a solvent, e.g. ketones, chlorinated hydrocarbons, aromatic hydrocarbons, higher ethers, dimethyl sulphoxide, sulpholane, esters or carbonamides. Water produced during the reaction is eliminated by a conventional method, e.g. distillation, use of a water separator or drying tube. After reaction the solvent is removed and the 3-methyl cephem carboxylic acid ester is isolated by conventional procedures. Phosphonium salts of Formula (3) as defined hereinbefore, e.g. 1-azetidine-2-ono-methoxycarbonylmethyl - triphenyl - phosphonium p - toluenesulphonate having 4-methyl or 4,4-dimethyl on the azetidine moiety, are prepared by the following procedure (in which the various symbols are as previously defined):- (a) An acid amide or lactam of formula (e.g. 4-methyl- or 4,4-dimethyl-azetidine-2-one, #-caprolactam or N-methylacetamide) is reacted with a glyoxyl ester of formula wherein R<SP>0</SP> is unsubstituted or substituted alkyl having up to 8 carbons (e.g. glyoxylic acid methyl ester methyl-semi-acetal), to give a derivative of a hydroxyacetic acid ester of formula e.g. 1 - (4 - methyl - or 4,4 - dimethyl - azetidine-2-ono)-hydroxyacetic acid methyl ester. (b) The said derivative is reacted with a halogenating agent (thionyl chloride) in the presence of an acid-binding agent to give a corresponding derivative of a halogenoacetic acid ester of formula: (c) The latter compound is reacted with a phosphine of formula (e.g. triphenyl phosphine) to give a phosphonium salt of formula wherein X- is a halogen ion. The halogen ion may be replaced by an anion of a different acid by treating the salt with a hydrohalic acid acceptor (e.g. NaOH), and reacting the resulting ylid with the different acid, e.g. p-toluenesulphonic acid.