Diels-Alder reactions of 1,2,4-triazines with cyclic vinyl ethers

Article abstract of DOI:10.1016/S0040-4020(01)82377-2

The Diels-Alder reaction of 1,2,4-triazines with cyclic vinyl ethers leads to a range of substituted pyridines with hydroxyalkyl and oxoalkyl side chains. With dihydrofuran the aromatization of the 1:1 adduct is inhibited by conformational factors and this allows 2:1 adducts to be isolated. Different regioselectivity is observed in the 2:1 adducts formed from ethyl 5-phenyl-1,2,4-triazine-3-carboxylate 1f and from ethyl 5,6-diphenyl-1,2,4-triazine-3-carboxylate 1b. An X-ray crystal structure of the 2:1 adduct 5 formed from 2,3-dihydrofuran and 1b is reported.