The development of a general catalytic asymmetric aldehyde α-alkylation reaction constitutes a major challenge in organic synthesis. Here, we report the first and successful approach toward its solution:(S)-α-methyl proline catalyzes the intramolecular alkylation of various halo aldehydes to the corresponding formyl cyclopentanes,-cyclopropanes, or- pyrrolidines in excellent yields and enantioselectivities. Most remarkably, racemization, ...
