We report an iridium-catalyzed stereoselective cyclization of aryl alkynes with tethered esters and imides to give silyl-protected O,O- and N,O-acetals. The optimized conditions afford chiral 5- and 6-membered heterocycles in excellent ee and moderate to high dr and can be isolated chromatographically as single diastereomers. A variety of esters, including acetates, formates, benzoates, and pivalates, can be employed to give functionalized tetrahydrofuran derivatives. Additionally, phthalimide- and maleimide-containing substrates give stereodefined nitrogen-containing bi- and tricyclic fused-ring products with potential applications in natural product synthesis, as illustrated by the synthesis of a known intermediate en route to furopyrrolizidine alkaloid UCS1025A.
