PHOTOCHEMICAL-REACTIONS OF SULFIDE-CONTAINING ALKYL PHENYLGLYOXYLATES(VOL 53, PG 7165, 1997)

Ethylthioalkyl phenylglyoxylates (2) underwent regioselective photocyc lization to produce up to 13-membered ring thiacyclols (3) in good yie lds. Cyclization occurred between the excited carbonyl group and the c arbon alpha to the sulfur on the remote side. Increasing the number of methylenes placed between the carbonyl group and the sulfide appears to make intermolecular hydrogen abstraction induced reductive dimeriza tion and intramolecular Norrish Type II more competitive, resulting in lower yields of 3. The remote cyclization can be rationalized by a ph otoinduced electron transfer from the sulfur atom to the excited carbo nyl group followed by proton transfer and subsequent cyclization of th e resulting biradical. Rate constants for electron transfer increase a s the chain connecting the electron donor and acceptor becomes longer and more flexible. (C) 1997 Elsevier Science Ltd.