Bismuth(III) Chloride Catalyzed Cycloisomerization of Enynes

Several simple bismuth(III) salts were screened for the suitability to catalyze the cycloisomerization of enynes. Among them, BiCl3 gave the best results. Under the optimized reaction conditions, eight substrates were studied, and acceptable to excellent isolated yields were obtained. Consistent with data in the literature, electron-deficient alkynes were found to be better substrates for the reaction than electron-rich ones. Because BiCl3 is readily available, inexpensive and environmentally benign, this soft Lewis acid catalyzed isomerization reaction is expected to be a good choice for organic chemists to prepare pyrrolidine derivatives. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)