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<triisopropylsilyl<tribenzylsilyl). The ratio of the diastereomeric products was proportional to the size of the silyl group, with the largest, tribenzylsilyl, giving the best ratio of 10:1. The expected stereochemistry was confirmed by X-ray crystallography.