Studies on the niobium pentachloride-mediated nucleophilic additions to an enantiopure cyclic N-acyliminium ion derived from (S)-malic acid

Abstract

The nucleophilic addition of several nucleophiles (allyltrimethylsilane, silyl enol ether from acetophenone, indole and N-sulfonylindole) to the enantiopure cyclic N-acyliminium ion 1a, derived from (S)-malic acid, promoted by niobium pentachloride is described. The products were obtained in good yields and in variable diastereoselectivities depending on the steric bulkiness of the nucleophile. The best results were obtained with the addition of indoles. ©2005 Sociedade Brasileira de Química.