The Diels–Alder reaction of 4-methoxy-7-hydroxyisobenzofuran with methyl vinyl ketone; a general method for identification of some regioisomeric α-naphthols

Two regioisomeric α-naphthols 14 and 15 obtained by aromatization of the methyl vinyl ketone adducts of an unsymmetrical isobenzofuran 9 are differentiated from each other by the observation of significant upfield shifts of the peri proton resonances in the 1H nmr spectra of their acetates 16 and 17. Such upfield shifts of 0.3–0.6 ppm appear to be a general phenomenon and are probably due to the anisotropic effect of the acetate carbonyl group.