Substituent Effects on Regioselectivity in the Photorearrangement of a Few Naphthobarrelenes

The photorearrangement of a few 9,10-disubstituted-naphthobarrelenes to the corresponding naphthosemibullvalenes has been examined. It was observed that the regioselectivity in these photoisomerizations depends on the relative stabilities of the diradical intermediates. AM1 semi-empirical calculations are in support of this view. Thermal transformation of the naphthosemibullvalenes gave the corresponding water added naphthopentalenofurans, in nearly quantitative yields.