The X-ray detd. structure of the title compd. I is reported; it was found that the annelated bonds are the longest obsd. in a benzene deriv. [1.540(5) .ANG.]; ab initio calcns. (at the B3LYP/6-31G* and MP2/6-31G* levels of theory) were used in order to understand the electronic and structural properties of the compd.