Rhodium-Catalyzed Asymmetric Reductive Cyclization of Alkynals

Significance

Transition-metal-catalyzed cyclizations of alkynals have been extensively studied. Nickel, rhodium, ruthenium, and titanium have been reported to catalyze reductive cyclizations of alkynals efficiently, leading to cyclic allylic alcohols with a trisubstituted alkene component. Reported here is a novel asymmetric reductive cyclization of heteroatom-linked 5-alkynals 1 with heteroatom-substituted acetaldehydes 3 using a cationic rhodium(I)/(R)-H₈-BINAP complex as catalyst. The cyclic allylic ester products 2 and 4 can be obtained in good yield and excellent ee.