Asymmetric Brønsted acid-catalyzed nazarov cyclization of acyclic α-alkoxy dienones.

A Brønsted acid-catalyzed asymmetric Nazarov cyclization of acyclic α-alkoxy dienones has been developed. The reaction offers access to chiral cyclopentenones in a highly enantioselective manner. The reaction is complementary to our previously reported Brønsted acid-catalyzed electrocyclization reactions, which provided differently substituted optically active cyclopentenones with a fused tetrahydropyrane ring in good yields and with excellent enantioselectivities.