Some studies on proximal addition–elimination procedures in intermolecular carbon–carbon bond-forming free radical reactions. Convenient synthesis of ethyl (E)-(ethyl 2,3,6,7,8-pentadeoxy-α-D-erythro-nona-2,7-dienopyranosid)uronate

Abstract

Et₃B-Induced hydrostannation of ethyl propiolate with tributyltin hydride afforded a mixture of ethyl (Z)- and (E)-3-(tributylstannyl)propenoate which, after purification, could be used as such in radical carbon–carbon bond-forming reactions with iodides as the sources of the carbon radicals. The radical-coupling reactions took place without significant loss of yield or stereoselectivity when compared with the same reactions carried out with the pure (Z)-stannylacrylate. Use of ethyl (Z)-3-(phenylsulfanyl)propenoate in the presence of carbon-centred radicals, generated with Bu₃SnH from alkyl iodides, resulted in the formation of reduced and coupled products where the intermediate β-phenylsulfanyl radicals had experienced hydrogen transfer from Bu₃SnH rather than 1,2-elimination of phenylsulfanyl radicals.