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. Th ese reactions constitute catalytic asymmetric propionate aldol additions. A n optically active Al(III)-triamine complex (10 mol %) catalyzes the di(iso propyl)ethylamine-mediated cyclocondensation of propionyl bromide and a var iety of aldehydes to afford beta-lactone adducts with uniformly high enanti oselection (90 --> 98% ee), diastereoselection (74 --> 98% de), and chemica l yields (78-90%). Lactone ring opening reveals that the enantiomerically e nriched beta-lactones act as surrogates for syn propionate aldol adducts.