Palladium-catalyzed carbonylative coupling of iodobenzene and 2-methyl-3-butyn-2-ol under biphasic conditions: Formation of furanones

Carbonylative coupling of iodobenzene and 2-methyl-3-butyn-2-ol (4) in aqueous NaOH/benzene was carried out by using Pd(OAc)(2)/Ph3P/Bu4PBr (A) and Pd(OAc)(2)/Ph2P(m-C6H4SO3Na) (B) as catalyst. In sharp contrast with a homogeneous Et3N solution, this biphasic solvent system gives 3-isopropylidene-5-phenyl-2(2H)-furanone (1) in a moderate yield. The other carbonylated products are 2,2-dimethyl-5-phenyl-3(2H)-furanone (2) and benzoic acid. The formation of 1 is explained by the following sequential reactions; carbonylative coupling of iodobenzene with 4 to form 4-hydroxy-4methyl-1 -phenyl-2-pentyn-1-one (6), hydrogenolysis of 6 to 4-methyl-1-phenyl-2,3-pentadien-1-one (8) and its cyclocarbonylation to 1. Catalyst A gives 1 in a higher yield than B. (C) 1998 Elsevier Science B.V.