PALLADIUM-CATALYSED CYCLISATION OF 2-SUBSTITUTED HALOGENOARENES BY DEHYDROHALOGENATION

Article abstract of DOI:10.1016/S0040-4020(01)91149-4

Cyclodehydrohalogenation mediated by various palladium catalysts and solvents with different bases (the most generally satisfactory system being palladium(II) acetate in NN-dimethylacetamide (DMA) with sodium carbonate as base) has been examined as a route to some heterocyclic systems.Whereas dehydrogenative cyclisation processes require stoichiometric amounts of palladium(II) reagent, the present procedure involves only catalytic amounts (0.1 molar proportion, or less), of palladium compound.The preparation of dibenzofuran, carbazole, fluorenone, 6H-dibenzo<1,2>thiazine-5,5-dioxide, 6H-dibenzopyran and benzofurano<2,3-b>pyridine derivatives is described.The cyclisation of 3-benzamido-2-chloropyridine to 6-hydroxybenzo<1,5>naphthiridine illustrates the regiospecificity of the process.