Synthesis of pentasubstituted pyridines. Cycloadditions of N-vinylic heterocumulenes with 1-(N,N-diethylamine)prop-1-yne

Article abstract of DOI:10.1016/S0040-4020(97)00126-9

The reactions of N-vinyl carbodiimides 4 and 5, and N-vinyl ketenimine 6 with ynamine 7 in THF, chloroform, toluene, and xylenes at, respectively, 0 °C, 25 °C, 100 °C, and 140 °C is shown. Pentasubstituted pyridines 8, 9, 11, and 12 are obtained in very high yields through thermally controlled [2+2] or [4+2] competitive processes. Additionally, when the temperature is raised the N-vinyl heterocumulenes 5 and 6 undergo an electrocyclic ring closure of six electrons driving to isoquinolines 10 and 13, respectively.