Title: The First Example of Cation Radical Induced Ether Cleavage of Benzyl Phenyl Ether
Abstract:In a continuation of our work with benzyl phenyl ether (1), in acetonitrile at room temperature, it was found to undergo oxidative C-O bond cleavage by the thianthrene cation radical (Th+•ClO4‒). As f...In a continuation of our work with benzyl phenyl ether (1), in acetonitrile at room temperature, it was found to undergo oxidative C-O bond cleavage by the thianthrene cation radical (Th+•ClO4‒). As far as the authors are aware, reactions of ether with cation radicals have not been reported, and as such, they offer the first examples of cation radical-induced ether cleavage. Generally, ethers react only reluctantly with bases, reducing agents and oxidizing agents. The C-O cleavage of benzyl phenyl ether typically occurs by heating with one equivalent of acid, through a SN1 pathway given the relative stability of the benzyl cation being formed; this is followed by C-O cleavage. It has been found that 1 reacts quantitatively with Th at a 1:2 (1:Th) stoichiometry to give quinonoids (3), N-benzylacetamide (4), and thianthrene (Th). The simplest representation of the reaction is given in Scheme 1. The products yielded were determined by quantitative GC and GC/MS analyses. NBenzylacetamide (4) was isolated in a yield of 87.4%, 3 (100%), Th (96.4%), phenol (1.01%), and trace amounts of ThO. A mechanism that fits the formation of such products involves the initial complexation of Th with 1 (eq 5) to produce a species more easily oxidized than Th, where electron transfer (eq 6) produces a thianthrene dication-benzyl phenyl ether complex (Th-1) that undergoes a rate-determining bond formation with expulsion of a proton (eq 7) to product 2. Benzyl cations are subsequently formed by SN1 loss of 3 from 2. Benzyl cations then react with the acetonitrile solvent, to give a Ritter-type intermediate (C6H5CH2N=CMe), which then reacts with water during work-up to give 4.Read More