Fries rearrangement of 2‐, 3‐ and 4‐methoxyphenyl 3‐methylbut‐2‐enoates 3‐5 in methanesulfonic acid, polyphosphoric acid, aluminum chloride and under photochemical conditions have been studied. The outcome of the reactions was determined by the substitution pattern in the starting products and the reaction conditions used. Under Lewis acid catalysis, acylation accounted for the major components of the reaction mixtures, leading to the formation of indanones and 2,3‐dihydro‐4H‐1‐benzopyran‐4‐ones respectively in the case of o‐ and m‐esters 3 and 5, whereas alkylation to afford dihydrocoumarins was the favored path for p‐ester 5. On the other hand, o‐acylation was in all cases the major reaction course in the photochemical rearrangement.
Treatment of 2,2‐dimethyl‐2H‐1‐benzopyrans 5 with a m‐chloroperoxybenzoic acid‐trifluoroacetic acid mixture and subsequent short path bulb to bulb vacuum distillation of the crude 3,4‐hydroxyesters 6 formed afforded title compounds in good yields. Suppression of trifluoroacetic acid was required when using 2,2‐di‐methyl‐2H‐1‐benzopyrans with electron donating substituents such as precocenes, as starting compounds.
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