Formation of Isdbenzenes by Thermal Isomerization of l,3-hexadiene-5-yne Derivatives

摘要

The cyclization of l,3-hexadiene-5-yne (1) to benzene (3), first described in the late 1960s, has proven in recent years to be a useful reaction for preparing bowl-shaped, nonalternating polycyclic arenes (fullerene fragments). The activation parameters for the formation of 3 from 1 were determined, and the electrocyclic formation of 1,2,4-cyclohexatriene (2, isoben-zene) was suggested as the first step. As this highly reactive benzene isomer has recently been prepared by treatment of the dibromocarbene adduct of 1,3-cyclopentadiene with methyl-lithium at -30 °C by Christl et al., the question arises whether 2 and its derivatives are also thermally accessible from 1 and related hydrocarbons. The experiments described here show that this is indeed the case.