Relay Catalysis: Enantioselective Synthesis of Cyclic Benzo-Fused Homoallylic Alcohols by Chiral Bronsted Acid-Catalyzed Allylboration/Ring Closing Metathesis

摘要

Six- and seven-membered benzo-fused cyclic homoallylic alcohols can be readily synthesized by a tandem chiral Br0nsted acid-catalyzed allyl (crotyl)boration/ring closing metathesis sequence performed under orthogonal relay catalysis conditions. Excellent enantio- and diastereoselectiv-ities are obtained in most of the cases. In addition, the parent crotylboration/RCM process is also described. The required substrates, ortho-vinylbenzal-dehydes, are readily available in one step from commercially available starting materials. Both catalysts and reactants are also available from commercial suppliers. The reaction shows broad functional group compatibility and is also suitable for hetero-aromatic substrates. Substitution at any position of the aromatic ring is tolerated;; however, substitution at position 6 results in a substantial drop in enantio-selectivity.