Cobalt-Stabilized Propargylic Oxocarbenium Ions Enable Direct and Asymmetric Nickel(II) Catalyzed Aldol-Like Reactions

High Resolution Image Download MS PowerPoint Slide We describe a direct and asymmetric aldol-like reaction between a wide range of N -acyl-1,3-oxazolidine-2-thiones and cobalt-protected propargylic acetals catalyzed by a chiral nickel(II) complex leading to syn β-alkoxy derivatives. This overcomes longstanding limitations associated with acetals from aliphatic aldehydes, selectively providing syn aldol adducts in excellent yields as single stereoisomers (dr >97:3, er up to >99:1). Furthermore, the cobalt fragment enables downstream intramolecular Pauson-Khand cyclizations, granting rapid access to densely functionalized bicyclic architectures.