Access to trans-3,4-dihydroxy-2-alkylpyrrolidines and piperidines by use of stereodefined cyclic N,O-acetals as a diversity-generating element.

A highly efficient and stereoselective synthetic pathway towards trans-3,4-dihydroxy-2-alkylpyrrolidines and piperidines is described. The nature of the protecting groups on the hydroxyl moieties played a crucial role on the trans selectivity. By using this method, a concise total synthesis of (-)-2-epilentiginosine has been achieved.