The photochemistry of alkyl 2-(Naphthalenyl)ethenylbenzoates: Photodehydrocyclization and photodimerization products and their structural elucidation by ¹H and ¹³C N.M.R.

Abstract

Irradiation of alkyl 2-[2-(naphthalen-1-yl)ethenyl]benzoates in benzene gave the photodehydro-cyclization product, the chrysenecarboxylates (3) as well as two of the photodimerization products, the cyclobutanes (6) and (7). Similarly, irradiation of alkyl 2-[2-(naphthalen-2-yl)ethenyl]benzoates furnished the benzo[c]phenanthrenecarboxylates (4) and the cyclobutanes (8) and (9). Photodehydro-cyclization appears to be favoured over the photodimerization in more polar media. Complete analyses of ¹H and ¹³C n.m.r. spectra of some of these compounds are presented along with the spectra of the parent chrysene for comparison. The structures and the stereochemistries of all the products obtained were determined principally from these n.m.r. analyses.