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-ALPHA-D-ERYTHRO-NONA-2,7-DIENOPYRANOSID)URONATE

Et(3)B-lnduced 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 Bu(3)SnH from alkyl iodides, resulted in the formation of reduced and coupled products where the intermediate beta-phenylsulfanyl radicals had experienced hydrogen transfer from Bu(3)SnH rather than 1,2-elimination of phenylsulfanyl radicals.