Donor/Acceptor-Stabilized 1-Silaketene: Reversible [2+2] Cycloaddition with Pyridine and Evolution by an Olefin Metathesis Reaction

Abstract : Thereactionofsilacyclopropylidene 1 with benzal-dehyde generates a1-silaketene complex 2 by af ormal atomic silicon insertion into the C=Ob ond of the aldehyde. The highly reactive 1-silaketene 2 undergoes ar eversible [2+ +2] cycloaddition with pyridine to give sila-b-lactam 3.O f particular interest, in the presence of 4-dimethylaminopyri-dine (DMAP), 1-silaketene complex 2 evolves througha ni n-tramolecular olefin metathesis reaction, generating an ew 1-silaketene complex 8 and cis-stilbene. Theoretical studies suggest that the reaction proceeds through the formation of at ransient silacyclobutanone, af our-membered-ring intermediate , similar to that proposed by Chauvin and co-workers for the transition-metal-based olefin metathesis.