1,3-Didehydrobenzene (m-Benzyne)

摘要

Of the three isonienc didebydrobenzenes, only 1,2-didehy-drobenzene (1) has been characterized unequivocally by direct spectroscopic methods. The only derivative of 2 that has been characterized by matrix IR spectroscopy is 2,4-didehydrophenol. Earlyreports on the UV/ Vis spectroscopic characterization of 2 and 3 are questionable, since the reaction conditions and reported properties suggest that a more stable isomer, such as enediyne 4. was observed. A barrier of only 19.8 kcalmol~(-1) was determined for the ring opening of 3 by Roth et al., which compares well with barriers of 19.4 and 20.5 kcalmol~(-1) for this reaction calculated at the CCSD(T) level of theory by Kruka and Cremer. Flash vacuum pyroiysis of both 1,3-diiodobenzene (5) and isophthaloyl diiodide (6) produced 4 as the principal product, which suggests that 2 also undergoes thermal nng opening to give 4 (Scheme 1).