Cyclocondensation of 3(2H)-benzo[b]thiophenone and oxidation products obtained during these reactions

The cyclocondensation of 3(2H)-benzo[b] thiophenone under acidic conditions has been studied. The symmetrical cyclotrimer tris(benzo[b]thieno)[2,3:2',3':3',2']benzene was formed and under certain conditions also a rearranged cyclotrimer, tris(benzo[b]thienyl)[2,3:2',3':3',2']benzene.The formation of cyclotrimers was accompanied by oxidative coupling products involving the initially formed dimeric compound, 3-hydroxy-2,3-bibenzo[b]thienyl. During several of these reactions, a novel heterocycle, tris(benzo[b]thieno)[3,2-b:2',3'-d:2',3'-f]oxepin, was formed. The products were studied by mass spectrometry and fragmentation pathways were determined by a linked scanning technique.