The Fries Rearrangement of Tolyl Phenylacetates -Studies on the Fries Rearrangement. II.-

Abstract

The Fries rearrangement of ο-tolyl phenylacetate[1] with anhydride aluminium chloride in boiling chlorobenzene gave 4-hydroxy-3-methylphenyl benzyl ketone [8] (58.0%) together with a small amount of 2-hydroxy-3-methylphenyl benzyl ketone [9]. The reverse Fries rearrangement of [9] into [1] with the same catalyst took place more readily than the conversion from [8] to [1], to which the low ortho-para ratio ([9]/[8]) in the Fries rearrangement of [1] seems to be ascribable (Fig.1, Table 1 and 4).
The yield of 2-hydroxy-4-methylphenyl benzyl ketone [15] from m-tolyl phenylacetate [2] in boiling nitromethane increased with the reaction time, while that of 4-hydroxy-2methylphenyl benzyl ketone [16] [decreased in a reverse manner during the reaction of[2]]. Consequently, the high ortho-para ratio ([15]/[16] =15.3) was obtained after 3-hours' reaction (Fig.2 and Table 2).
The yield of 4-hydrox y-3, 5-dimethylphenyl benzyl ketone [13] from 2, 6-xylyl phenylacetate [5] was higher than those of 2-hydroxy-3, 5-dimethylphenyl benzyl ketone [14] and 2hydroxy-5-methylphenyl benzyl ketone [17] from 2, 4-xylyl phenylacetate [4] and p-tolyl phenylacetate [3], respectively, under the same conditions. Those results seem to indicate that a rate of p-migration is faster than that of ortho-migration in the AlCl₃-catalyzed Fries rearrangement of tolyl phenylacetate (Table 3).
When [4] and [5] were boiled with AlCl₃ in toluene, respectively, the yield of [14] and [15] reduced and 2-tolyl benzyl ketone [6] and 4-tolyl benzyl ketone [7] were obtained in each case (Table 3). Considering the remarkable difference of the yields in the tolyl ketones and product ratio ([6]: 7.0% and [7]: 4.1% derived from [4], [6]/[7] =1.71. [6]: 3.8% and [7]: 47.2 % derived from [5], [6]/[7] =0.08), the para-rearrangement seems to proceed via an intermolecular migration and the ortho-migration occurs in an intramolecular manner.