Enzyme-mediated preparation of enantioenriched forms of trans- and cis-p-menthan-1,8-dien-5-ol

The synthesis of the trans-p-menthan-5-ol (+/-)-1 was carried out by Diels-Alder cycloaddition of 3-keto-1-butenyl-acetate 3 with isoprene followed by Wittig methylenation. PS lipase resolution of the alcohol afforded acetate (-)-5 with 98% ec, which was hydrolysed to give (-)1. Alternatively, enzymatic hydrolysis of a keto ester followed by Wittig methylenation and hydrolysis afforded the same alcohol with an ee of 86%. The cis-p-menthan-5-ol (-)-2 was obtained by Swern oxidation of (-)-1. followed by diastereoselective reduction with L-Selectride without lost of enantiomeric excess.