Stereoselective Synthesis of Polysubstituted Tetrahydropyrans by Radical Cyclization of Epoxides using a Transition‐Metal Radical Source

Abstract

AbstractEpoxyalkyl propargyl ethers 3a–f and allyl epoxyalkyl ethers 6a–c smoothly undergo radical cyclization reactions using a titanium(III) species (Cp2TiCl) as the radical initiator to form polysubstituted tetrahydropyrans 4a–f and 7a–c in good yields and with high diastreoselectivity. The titanium(III) species was prepared in situ from commercially available titanocene dichloride and Zn dust in THF. On the other hand, the epoxyalkyl propargyl ethers 3g and 3h furnished the spirocyclic ethers 4g and 4h, respectively, on radical cyclization reaction as the sole products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)