Thermal Reorganizations of 1,2:3,4-Dibenzotropilidene (5H-Dibenzocycloheptene), 7,7'-Bi(1,2:3,4-dibenzotropyl) cycloheptenyl)>, and the 1,2:3,4-Dibenzotropyl (Dibenzocycloheptenyl) Free Radical

Article abstract of DOI:10.1021/jo00195a032

1,2:3,4-Dibenzotropilidene (5H-dibenzocycloheptene, 8) has been shown to thermally produce phenanthrene (12), 9-methylphenanthrene (13), 9,10-dihydrophenanthrene (14), and 1,2:3,4-dibenzocycloheptadiene (6,7-dihydro-5H-dibenzocycloheptene, 15).With added naphthalene, to trap the extruded one-carbon species, 1,2-benzotropilidene (16), α-methyl- and β-methylnaphthalene (17 and 18), 1,2-benzo-1,3-cycloheptadiene (19), and benzocycloheptene (20) were also produced.Reaction of 1,2-benzotropilidene with phenanthrene produced 1,2:3,4-dibenzotropilidene (8) and naphthalene, showing the reversibility of this thermal carbon extrusion reaction. 7,7'-Bi(1,2:3,4-dibenzotropyl) <5,5'-bi(5H-dibenzocycloheptenyl), 10> was prepared by VCl2 reduction of the 1,2:3,4-dibenzotropylium cation.Thermally it underwent the same reactions as 8, demonstrating that it is the 1,2:3,4-dibenzotropyl (dibenzocycloheptenyl) free radical (9) which lost a carbon atom (CH group) to the aromatic acceptor.At 200 deg C the dimer 10 produced significant quantities of 9-methylphenanthrene (13), shown not to arise from 8, in addition to phenanthrene, 12.Mechanisms for the thermal transfer of a CH group from 9 to an aromatic acceptor and for the production of 13 from 9 are presented.