Diastereoselective Intramolecular (3+2) Cycloadditions of Epoxy and Aziridinyl Enolsilanes

Abstract

Epoxy and aziridinyl enolsilanes undergo inter- and intramolecular (4+3) cycloadditions with dienes such as cyclopentadiene and furan, to produce cycloheptanoid cycloadducts in high yields and with good dr and ee.1 Herein, we report a diastereoselective intramolecular (3+2) cycloaddition reaction of epoxy and aziridinyl enolsilanes with olefins. This reaction results in perhydroindane derivatives bearing four contiguous stereocenters. Moreover, asymmetric cycloadducts are obtained with retention of ee from enantiomerically pure aziridines (Equation 1) and epoxides (Equation 2). These cycloadditions proceed by a stepwise mechanism, through the intermediacy of an activated epoxide or aziridine 4, and stabilized carbocation X. Dearomative intramolecular (3+2) cycloadditions of indoles also occur with activated epoxy and aziridinyl enolsilanes, to afford highly functionalized cyclopentaindoline compounds bearing four contiguous stereocenters in good yields in one step (Equation 3).