Catalytic Asymmetric Propionate Aldol Reactions via Acyl Halide−Aldehyde Cyclocondensations

Catalyzed asymmetric acyl halide−aldehyde cyclocondensation (AAC) reactions afford highly enantiomerically enriched 3,4-disubstituted-2-oxetanones. These reactions constitute catalytic asymmetric propionate aldol additions. An optically active Al(III)-triamine complex (10 mol %) catalyzes the di(isopropyl)ethylamine-mediated cyclocondensation of propionyl bromide and a variety of aldehydes to afford β-lactone adducts with uniformly high enantioselection (90 → 98% ee), diastereoselection (74 → 98% de), and chemical yields (78−90%). Lactone ring opening reveals that the enantiomerically enriched β-lactones act as surrogates for syn propionate aldol adducts.