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

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).