α,3-didehydro-5-methyl-6-hydroxytoluene:: Matrix isolation of a diradical related to the neocarzinostatin chromophore

UV photolysis of 2,6-dimethylcyclohexa-2,5-dien-1-on-4-ylidene (4), matrix isolated in argon at 10 K, results in the formation of a labile species which is characterized as a,3-didehydro-5-methyl-6-hydroxybenzene (5) by comparison of the experimental IR spectrum with calculations at the ROSS-BLYP/6-31G(d,p) level of theory. This assignment is confirmed by isotopic labeling and by investigating the subsequent photochemistry of 5, which leads to 3-hydroxy-4-methylhepta-1,2,4-trien-6-yne (6). The ring opening of diradical 5 to eneyne-allene 6 corresponds to the reversion of a Myers cyclization.