Diastereoselectivity during 2-pyridone photo-[4+4] cycloaddition. The tribenzylsilyl protecting group

The use of a silyloxy group as a stereocontrol element on the most distant carbon of a pyrindinone during intermolecular [4+4] photocycloaddition was tested using silyl groups varying in size (tert-butyldimethylsilyl < triiso propylsilyl < tribenzylsilyl). The ratio of the diastereomeric products was proportional to the size of the silyl group, with the largest, tribenzylsi lyl, giving the best ratio of 10:1. The expected stereochemistry was confir med by X-ray crystallography. (C) 2001 Elsevier Science Ltd. All rights res erved.