Sequential Diastereoselective Addition of Allylic and Homoallylic Grignard Reagents to 2‐Acyl‐perhydro‐1,3‐benzoxazines and Ring‐Closing Metathesis: an Asymmetric Route to Azepin‐3‐ol and Azocin‐3‐ol Derivatives

Chiral 2‐acyl‐3‐allyl‐substituted perhydrobenzoxazines derived from (–)‐8‐aminomenthol react with allyl or homoallyl Grignard reagents to provide the corresponding tertiary alcohols in very good yields and with excellent diastereoselectivities. The 1,8‐ and 1,9‐azadienes prepared in this way participate in RCM reactions to give good yields of seven‐ and eight‐membered nitrogen heterocycles. The yields of the RCM reaction increased when the hydrochlorides were used instead of the neutral azadienes. The removal of the chiral adjuvant allowed the preparation of enantiopure azepin‐3‐ol and azocin‐3‐ol derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)