Synthesis and Structure of 2,2′-Dihydroxybenzophenones and 1,8-Dihydroxyfluorenones

Derivatives of 2,2′-dihydroxybenzophenone and 1,8-dihydroxyfluorenone are interesting because their structures juxtapose a carbonyl group and two hydroxyl groups, thereby permitting them to be used to study the double electrophilic activation of carbonyl compounds by Lewis and Brønsted acids. Efficient syntheses of selected 2,2′-dihydroxybenzophenones 2a,b and 1,8-dihydroxyfluorenones 3a—c are described. Spectroscopic and X-ray crystallographic studies show that the carbonyl oxygen atom in each series of compounds accepts two approximately symmetric intramolecular hydrogen bonds. This observation illustrates the ability of carbonyl compounds to interact simultaneously with multiple electrophilic sites.