Diastereoselective formation of anellated tetrahydrofurans using a nitrate radical induced oxidative, self-terminating radical cyclization cascade

Addition of electrogenerated nitrate radicals to C=C triple bonds in the alkynyl ethers cis-7-9 and trans-8-9 yields anellated tetrahydrofurans 12-16 with high diasteroselectivity through a new type of an oxidative, self-terminating radical cyclization cascade. The reaction probably proceeds via an intramolecular, rate-determining hydrogen atom transfer in the vinyl radical of type 17a, and a subsequent diastereoselective 5-exo radical cyclization. Elimination of nitrogen dioxide terminates the reaction sequence. This reaction is a remarkable example for the creation of a C-O bond by intermolecular addition of an O-centered radical to a pi-system. (C) 1999 Elsevier Science Ltd. All rights reserved.