Ethynyltributyltin - A synthetic equivalent for acetylene, aryl, acyl and halogeno alkynes in [4+2] cycloadditions

Article abstract of DOI:10.1016/S0040-4039(98)00343-8

Ethynyltributyltin 2 cycloadds to 5-phenyl-1,2,4-triazine-3-carboxyclic acid methyl eater I to furnish mainly 4-tributylstannyl-6-phenyl-pyridine-2- carboxyclic acid methyl ester 3a besides a small amount of the 3- tributylstannyl isomer 3b. The tributyltin substituent of pyridine 3a can be replaced by Pd-catalyzed acylation and arylation, by halogenation and protonation to yield functionalized pyridines 4 - 7, which are not available by direct cycloaddition of the corresponding alkynes.