Cyclization of Aminocyclopropanes in Indole Alkaloids Synthesis

The regioselective and diastereoselective cyclization of acyliminium intermediates generated from aminocyclopropanes on unprotected indoles is presented. The recent results obtained in our group are compared with previous intermolecular reactions with aminocyclopropanes as well as with other cyclization methods involving iminium ions and unprotected indoles. A first speculative analysis of possible reaction mechanisms allows rationalizing the observed selectivity. The high potential of the method for the synthesis of natural alkaloids is demonstrated in the formal synthesis of aspidospermidine and the total synthesis of goniomitine.