N-oxides and related compounds. Part XXXIII. The mechanism of the acetic anhydride rearrangement of 2-alkylpyridine 1-oxides

Abstract

Reinvestigation of the reaction of [¹⁸O]acetic anhydride with alkylpyridine 1-oxides confirms the conclusion of Oae et al. that intramolecular scrambling of the oxygen atoms of the acetoxy-group occurs; however, investigation of a variety of 2-alkylpyridine 1-oxides indicates that an ion-pair rather than a radical-pair intermediate is involved. Thus, 2-cyclopentylmethyl- and 2-neopentyl-pyridine 1-oxide yield products rationally explained by the incursion of carbonium ion rearrangements, and 2-propylpyridine 1-oxide produces a considerable amount of 2-prop-1-enylpyridine.