6H-Dibenzo[b,d]pyrans. II. Boron Trifluoride Catalyzed Acylation of Hydroxy-6H-dibenzo[b,d]pyrans

The Friedel–Crafts acetylation of 3-hydroxy-6H-dibenzo[b,d]pyrans (1) with acetic acid in the presence of boron trifluoride is described. Representatives unsubstituted at C-1 acylate exclusively at C-2. A methyl or methoxyl substituent at C-1 directs acylation to the C-4 position. The identities of the individual isomers are established primarily on the basis of n.m.r. spectral interpretations.