Asymmetric synthesis of cyclopentanones through dual Lewis acid-catalysed [3+2]-cycloaddition of donor–acceptor cyclopropanes with ketenes

Abstract

When InBr₃-EtAlCl₂ (15–30 mol%) was used as a dual Lewis acid system to promote the formal [3+2]-cycloaddition of enantioenriched donor–acceptor cyclopropanes with ketenes, cyclopentanones were formed in good to excellent yields (84–99%, 18 examples), and with excellent transfer of chirality (15 examples, 90% ee to >99% ee).