Regioselectivity of Intramolecular Electrophilic Cyclization of 2-(Alkenylsulfanyl)thieno[2,3-d]pyrimidin-4(3H)-ones with p-Methoxyphenyltellurium Trichloride

3-Phenyl-2-(prop-2-en-1-ylsulfanyl)-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4(3H)-one reacted with 4-methoxyphenyltellurium trichloride in a regioselective manner to give angularly fused 1-{[dichloro(4-methoxyphenyl)-λ4-tellanyl]methyl}-4-oxo-5-phenyl-1,2,4,5,6,7,8,9-octahydrobenzo[4,5]thieno[3,2-e][1,3]thiazolo[3,2-a]pyrimidinium chloride. Electrophilic cyclization of 2-(prop-2-en-1-ylsulfanyl)- and 2-(2-methylprop-2-en-1-ylsulfanyl)-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4(3H)-ones with 4-methoxyphenyltellurium trichloride afforded linearly fused 3-{[dichloro(4-methoxyphenyl)-λ4-tellanyl]methyl}-2,3,6,7,8,9-hexahydro-5H-benzo[4,5]thieno[2,3-d][1,3]thiazolo[3,2-a]pyrimidin-5-one hydrochlorides. Regardless of the reactant ratio, the products were isolated as 1:1 complexes with 4-methoxyphenyltellurium trichloride.