Ring contraction through epoxide rearrangement: A formal synthesis of capsorubin

An eight-step synthesis of the cyclopentane keto-alcohol 2, which has previ ously been converted in one step into the carotenoid pigment capsorubin (1) is described. The key step in our synthesis is a stereospecific epoxide re arrangement with ring contraction, thus producing the cyclopentane ring fro m an epoxide of a cyclohexene.