Indium-catalyzed Conia-ene reaction for alkaloid synthesis

In(OTf)(3)-catalyzed cyclization of nitrogen- and oxygen-tethered acetylenic malonic esters provides various five- to seven-membered heterocycles in moderate to excellent yield, and the reaction proceeds with no racemization and complete E-selectivity in the case of chiral and nonterminal alkynes. The synthetic utility is demonstrated by the synthesis of (-)-salinosporamide A, a highly potent 20S proteasome inhibitor, and (+)-neooxazolomycin, a member of the oxazolomycin family of antibiotics.