Flash Vacuum Thermolysis of 5,6,8,9-Tetrahydro-4'-methylenespiro. The Intermediate Formation of Orthoparacyclophane

Article abstract of DOI:10.1021/jo00362a002

Flash vacuum thermolysis (FVT) of 5,6,8,9-tetrahydro-4'-methylenespiro<7H-benzocycloheptene-7,1'-cyclohexa-2',5'-diene> (2a) at 520-650 deg C yielded isomeric products 10 (26percent), 12a (14percent), and 19 (3percent) and 2,2'-dimethyldibenzyl (17, 22percent).The formation of these products from the primary intermediate, the diradical 3a, is discussed.It is concluded that 17 and 19 are formed via the intermediate <3,2>orthoparacyclophane (1a) which is unstable under FVT conditions.Attempts to investigate the regioisomer 2b of 2a were thwarted by the high reactivity of 2b even at room temperature.FVT of 4a, the 4'-keto precursor of 2a, yielded 31 (60percent); FVT of 4b gave 17 (80percent) and p-hydroxystyrene (30, 3percent).In the thermolysis of 4, cyclophanes are probably not involved