Gold-catalyzed cycloisomerization of α-aminoallenes to 3-pyrrolines optimization and mechanistic studies

The gold-catalyzed cycloisomerization of various alpha-aminoallenes affords the corresponding 3-pyrrolines in good to high chemical yields and - if the amino group is unprotected with complete axis-to-center chirality transfer. Diminished levels of chirality transfer were observed in cases of N-protected substrates, which may be the result of partial epimerization of the allene in the presence of the gold precatalyst. The low reactivity of the intramolecular hydroamination of unprotected a-aminoallenes with AuCl3 was improved by use of gold(I) halides as the precatalyst. Mechanistic studies suggest that a gold(l) compound (formed by oxidation of the aminoallene) is the catalytically active species even if the reaction is started with a gold(III) precatalyst. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).