Regioselectivity and Stereoselectivity in the Photodimerization of Rigid and Semirigid Stilbenes

Article abstract of DOI:10.1021/jo00041a035

The (2? + 2?)-photodimerizations of 2-phenylindene (1), 2-(4-methoxyphenyl)indene (9), and 5,10-dihydroindeno<2,1-a>indene (2) were investigated in a variety of homogenous and micellar solvents.Four isomeric photodimers were formed from 1 and 9: syn-head-to-tail, syn-head-to-head, anti-head-to-tail, and anti-head-to-head.Relative yields of these as well as syn/anti- and head-to-tail (ht)/head-to-head (hh) ratios were determined in various solvents and as a function of temperature.In 1 syn/anti ratios ranged from 1.07 to 1.62 ht/hh ratios from 0.88 to 1.28.In 9 syn/anti ratios between 0.83 and 2.55 and ht/hh ratios between 0.4 and 1.2 were found; preferred formation of anti and hh products was observed in micellar solvents as expected from preorientation of reactants.Two photodimers (ht and hh) were found upon irradiation of 2. ht/hh ratios ranged from 0.89 to 1.56.The variations of these ratios can be understood on the basis of a kinetic scheme, in which individual excimer states as precursors of the respective dimers are involved.