A facile synthesis of beta-(S-benzylmercapto)-beta, beta-cyclopentamethylene-propionic acid

The title compound is a key intermediate for the preparation of oxytocin and vasopressin antagonists. Using sodium benzylmercaptide instead of boron trifluoride etherate as catalyst gives a better than four fold overall improvement in yield of the title compound from ethyl cyclohexylideneacetate and benzylmercaptan. The preparation of the corresponding acid labile S-p-methylbenzylmercapto and S-p-methoxybenzylmercapto analogs is also described.