Photochemical Synthesis of Fused Tricyclic Compounds from Bis-6, 6'-(1, 3-dialkyluracilyl) sulfides

Abstract

Bis-6, 6'-(1, 3-dialkyluracilyl) sulfides (3) were synthesized by coupling of 6-chloro-1, 3-dialkyluracil (1) and 1, 3-dialkyluracil-6-mercaptide (2). Compounds (3) were found to undergo photochemical cyclization, giving rise to three types of isolable products with novel ring systems, namely, 1, 3, 6, 8-tetraalkyl [1, 4] dithiino [2, 3-d ; 5, 6-d'] dipyrimidines (4), 1, 3, 6, 8-tetraalkylthiopheno [2, 3-d ; 4, 5-d'] dipyrimidines (6) and the dihydro derivatives (8) of the latter. These compounds were fully characterized by 'H-NMR, mass spectral and elemental analyses. A plausible mechanism for this photocyclization of 3 to 6 and to 8 has been proposed.