A concise formal approach to the oxacephem skeleton from an intramolecular Peterson type olefination of N-[bis(trimethylsilyl)methyl]-β-lactams

Bis(trimethylsilyl)methylamine (BSMA): tool or toy?

Bis(trimethylsilyl)methylamine, BSMA, an original primary amine, was proven to be the source of a large variety of N-bis(trimethylsilyl)methylamino derivatives that otherwise have to be prepared indirectly. Because of the bulkiness of the bissilylmethyl group, regio- and stereoselectivities resulted in appropriated examples. Apart from the potential biological properties associated with the Si-C-N framework, these derivatives were powerful synthetic intermediates. Special emphasis was given to the chemistry of corresponding imines. Cleavage of Si—C bonds or abstraction of the methine proton afforded α-nitrogen carbanions in very mild conditions. Application of these results to the β-lactam chemistry allowed the introduction of new synthetic methodologies in this field. It results the (Me3Si)2CH- group could now be regarded as a Me3SiCH2- or a CH3- group or a proton equivalent.Key words: bis(silyl)methylamine, preparations, reactivity, nitrogen heterocycles, α-nitrogen carbanions.

Construction of Quaternary Stereogenic Centers via [2 + 2] Cycloaddition Reactions. Synthesis of Homochiral 4,4-Disubstituted 2-Azetidinones and Imine Substituent Effects on beta-Lactam Formation

A study on the asymmetric construction of quaternary stereogenic centers via [2 + 2] cycloaddition reaction of ketenes with ketimines is described. Reaction of achiral ketenes and chiral alpha-alkoxy ketone-derived imines resulted in formation of new beta-lactams as single diastereomers. The cycloaddition was extended to pyruvate imines, aralkyl ketone-derived imines, and dialkyl ketimines. In these cases the asymmetric induction was satisfactorily achieved using beta-silylalkanoyl ketenes and the Evans-Sjögren ketene. C,C-Bis (trimethylsilyl)methylamine ketimines derived from enolizable dialkyl ketones cleanly led to the corresponding C(4) disubstituted beta-lactams without deprotonation. Therefore, a general methodology for a convergent asymmetric synthesis of beta-lactams in which C(4) exists as a quaternary carbon is provided.