Synthesis and unusual selenium extrusion reaction of a cyclic triselenide

Reaction of (Z)-2,3-bis(2-lithiophenyl)-2-butene (10) with selenium gave 12,13-dimethyldibenzo [d,h]-1,2,3-triselenonine (3) rather than either 11,12-dimethyldibenzo [c,g]-1,2-diselenocine (2) or 13,14-dimethyldibenzo [e,i]-1,2,3,4-tetraselenecine (4). Thermolysis and photolysis of 3 gave 5a,10a-dihydro-5a,10a-dimethyldibenzo-[b,f] seleno [3,2-b] selenophene (12) via extrusion of a selenium atom and a novel intramolecular addition of arylselenyls to a double bond. Ab initio molecular orbital calculations and X-ray structural analyses are made to elucidate the reaction mechanism