Reaction of ‘myrcene–magnesium’ with esters, acetyl chloride, and acetic anhydride: formation of cyclopentenols and cyclopropane derivatives

Abstract

Addition of a series of esters to the ‘myrcene–magnesium’ complex at room temperature yielded a mixture of ketones [(1) and (2)] and a substituted cyclopentenol (3). The products (1) and (2) were formed by a 1,4-addition across the 1,3-diene system; cyclisation then yielded (3). With ethyl pivalate, the cyclopentenol is >90% of the product mixture, but (3) is almost the only product when the reaction with other esters is conducted at 65 °C. The importance of steric effects in the cyclisation was confirmed by the reaction of ethyl acetate with the magnesium complex of 1,4-diphenylbuta-1,3-diene to give only cyclopentenols. The reaction of the ‘myrcene–magnesium’ complex with acetyl chloride or acetic anhydride also yields cyclopropyl acetates, as a result of a 1,2-addition to the diene unit, followed by cyclisation and acetylation.