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.

A adição nucleofílica de vários nucleófilos (alilsilano, silil enol éter da acetofenona, indol e N-sulfonilindol) ao íon N-acilimínio enantiopuro 1a, derivado do ácido (S)-málico, promovida por pentacloreto de nióbio é descrita. Os produtos foram obtidos em bons rendimentos e em diastereosseletividades variáveis dependendo do volume estérico do nucleófilo. Os melhores resultados foram obtidos com a adição de indóis.