CONVENIENT SYNTHESIS OF VARIOUS TERHETEROCYCLIC COMPOUNDS BY PD(O)-CATALYZED COUPLING REACTIONS

Various terheterocyclic compounds containing thiophene, furan, selenophene, pyridine and thiazole rings have been obtained by the Pd(PPh3)4-catalyzed coupling of dihalo-substituted heterocyclic compounds with heterocyclic boronic acids, using sodium bicarbonate as base and a 1,2-dimethoxyethane - water mixture as solvent. In cases when the boronic acids were not available or easily deboronated, and/or the heterocyclic halo derivatives were unstable in alkaline solution, trialkylstannylheterocycles were used instead of boronic acids in the coupling with dihaloheterocycles, with THF as solvent and PdCl2(PPh3)2 as catalyst. The naturally occurring 3′-methoxy-2,2′:5′,2″-terthiophene was prepared by a copper-promoted nucleophilic substitution of 3′-iodo-2,2′:5′,2″-terthiophene, previously prepared by Pd(0)-catalyzed coupling of 2,3,5-triiodothiophene with 2-thiophene boronic acid. © 1990.