Method for enzymatic synthesis of the acid (7s) 3,4-dimethoxybicyclo [4.2.0] octa-1,3,5-triene 7-carboxylic acid or its esters, and application to the synthesis of ivabradine and its salts

A method of enzymatic synthesis of the compound of formula (I): wherein R represents a hydrogen atom or an alkyl group. Application to the synthesis of ivabradine and its addition salts with a pharmaceutically acceptable acid.