Staudinger preparation asymmetric. 3 lactams

SCHEME 10.11 Asymmetric Staudinger preparation of P-lactams directed by sugar-derived chiral auxiliaries. 

In 2002, the asymmetric synthesis of 3-substituted 3-hydroxy-p-lactams has been reported to be realized by metal-mediated l,3-butadien-2-ylation reactions between 1,4-dibromo-2-butyne and optically pure azetidine-2,3-diones [64]. This latter starting material was prepared via Staudinger reaction followed by sequential transesterification and Swem oxidation (Scheme 15), [65]. 

Polymer-bound P-lactams have been prepared via the ester enolate imine condensation route <02JOC8034>. On the other hand, an efficient asymmetric synthesis of 2-azetidinones was accomplished when chiral acid chlorides or chiral aldehydes were used in the polymer-supported Staudinger reaction <02TA905>. 

The addition of an acid chloride to an imine is an important method for the preparation of (3-lactams and is often referred to as the Staudinger reaction. The reaction allows a convenient and mild approach to the -lactam antibiotics and has therefore received considerable attention. Good stereoselectivity in favour of the cis 3,4-disubstituted product is common. For example, the p-lactam 182 was formed in reasonable yield by condensation of the acid chloride 180 and the imine 181 (3.120). The reaction is not thought to be a concerted cycloaddition with the ketene, but to take place via a zwitterionic intermediate. Almost complete asymmetric induction in the synthesis of -lactams by the Staudinger reaction using a chiral auxiliary or a chiral tertiary amine, such as benzoylquinine, has been reported. 

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