Intermediate Formation ofMetacyclophane on Flash Vacuum Thermolysis

Article abstract of DOI:10.1021/jo00254a021

Pyrolysis of 2,6-tetramethylene Dewar benzene (2a) under flash vacuum thermolysis (FVT) conditions at 400 deg C gave 6- and 5-methylindan (8a (2.5percent) and 10a (2.5percent), respectively) as well tetralin (5a) (45percent).These products indicate that <4>metacyclophane (1a) was formed in the gas phase, but it decomposed under the reaction conditions either via homolytic cleavage of one of the benzylic bonds to yield a diradical (6a) leading to 8a and 10a or it gave 5a via benzvalene intermediate (4a).Deuterium labeling supports the proposed mechanism.A very similar course of events was observed on FVT of <5>metacyclophane at 600 deg C; it yielded methyl-substituted tetralins (8c, 10c) as the sole products.The analogies and differences in the behavior of the two metacyclophanes are discussed.