Process for the preparation of isotretinoin

A process for the preparation of isotretinoin in a single step, which comprises:

• condensation of dienolate of methyl 3,3-dimethyl acrylate of Formula I:
• with β-ionylidene-acetaldehyde of Formula II:
• in a suitable solvent at a temperature between −60° C. to −80° C. for 1-2 hours to produce the intermediate lactone of Formula III, and
• raising temperature of the reaction mixture to 25° C. to 45° C. and stirring for 1-24 hours;
• followed by aqueous acidic work up to form isotretinoin of Formula IV:
• containing less than 0.1% of tretinoin impurity of Formula V: