Organocatalytic asymmetric synthesis of Si-stereogenic silacycles.

A strong and confined Brønsted acid catalyzed enantioselective cyclization of bis(methallyl)silanes provides enantioenriched Si-stereogenic silacycles. High enantioselectivities of up to 96.5:3.5 er were obtained for a range of bis(methallyl)silanes. NMR and ESI-MS studies reveal that the formation of a covalent adduct irreversibly inhibits turnover. Remarkably, we found that acetic acid as an additive promotes the collapse of this adduct, enabling full turnover. Experimental investigation and density functional theory (DFT) calculations were conducted to elucidate the origin of this phenomenon and the observed enantioselectivity. Among the diverse organosilicon compounds, Si-stereogenic silanes have recently demonstrated promising biological activities but only few protocols for the preparation of organosilicon compounds possessing a Si-stereogenic center exist in the literature. Here the authors show that a strong and confined Brønsted acid catalyzed enantioselective cyclization of bis(methallyl)silanes and provides enantioenriched Si-stereogenic silacycles. [ABSTRACT FROM AUTHOR]