Synthesis of 2,5-bis-arylpyridines by [4+2] cycloaddition of 1,4-bis aryl-2-aza-1,3-butadienes with electron-poor dienophiles

Tetrahydropyridines 4a, 4b, 4c and pyridines 7a, 7b, 7c, 9a, 9b, 9c were sy nthesized by a [4 + 2] cycloaddition between 1,4-bis aryl-2-aza-1,3-butadie nes and electron-poor dienophiles. Dimeric cycloadducts 6a, 6b, 6c, were al so isolated indicating a competition between the expected Hetero Diels-Alde r and a dimerization process.