Phosphorus-based reagents 16- member

Cyclopalladated complexes provide a potential use for regiospecifically controlled organic syntheses.1 Various substituents can be introduced onto the palladated carbon position by reactions of cyclopalladated complexes with various reagents.2-4 Cyclopalladation of aryl-substituted nitrogen or phosphorus bases has been performed mainly by use of [PdCl4]2- or PdCl2(NCPh)2 in the presence or absence of an acetate salt, but this method appears to have limit in applicability.5,6 Here, we describe a preparation of a rare six-membered cyclopalladated complex of 2-benzylpyridine by use of palladium(II) acetate,7 which seems to be a better starting material for syntheses of cyclopalladated species.6,7 Only five reports of six-membered cyclopalladated complexes have appeared.7,8... 

These reagents are usually prepared by treatment of a phosphine with an alkyl halide and successive addition of base, like BuLi or NaHMDS. Reaction with the ketone takes place by attack of the carbanionoid carbon of the ylide form on the electrophilic carbon of the carbonyl group via a four-membered heterocyclic transition state, the oxaphosphetane 35. The driving force for this transformation is provided by formation of the very strong phosphorus-oxygen bond. Subsequent collapse of the oxaphosphetane furnishes the desired exomethylene group under retention of geometry. 

About a decade ago 6-APA and 7-ADCA were mainly produced by chemical deacylation of penicillin G, penicillin V or phenylacetyl 7-ADCA, the last of which was derived from chemical ring expansion of oxidized penicillin G. As a result of the fact that these processes were rather complex and employed hazardous reagents, for example pyridine, phosphorus pentachloride, nitrosyl chloride and dichlorome-thane, alternative processes have been developed. Penicillin amidases (E. C. 3.5.1.11) catalyze the hydrolysis of the linear amide bond in penicillin molecules producing both the P-lactam nucleus, 6-APA and the corresponding side chain without affecting the P-lactam amide bond in the four-membered ring. Based on their substrate specificity the penicillin amidases are grouped into three classes[591 ... 

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