Diphenyl ether, Smiles rearrangement

Directed lithiation of aromatic compounds is a reaction of broad scope and considerable synthetic utility. The metalation of arenesulfonyl systems was first observed by Gilman and Webb and by Truce and Amos who reported that diphenyl sulfone is easily metalated at an orf/io-position by butyllithium. Subsequently, in 1958, Truce and coworkers discovered that metalation of mesityl phenyl sulfone (110) occurred entirely at an orf/io-methyl group and not at a ring carbon, as expected. Furthermore, refluxing an ether solution of the lithiated species resulted in a novel and unusual variation of the Smiles rearrangement and formation of 2-benzyl-4,6-dimethyl-benzenesulfinic acid (111) in almost quatitative yield (equation 78). Several other o-methyl diaryl sulfones have also been shown to rearrange to o-benzylbenzenesulfinic acids when heated in ether solution with... 

Gara A, Andersson K, Nilsson C, Norstrom A (1981), Chemosphere 10 365-390.. .Synthesis of halogenated diphenyl ethers and dibenzofurans - a discussion of specific isomers available" Gray AP, Cepa SP, Cantrell JS (1975), Tetrahedron Lett. 33 2873-2876.. .Intervention of the Smiles rearrangement in syntheses of dibenzodioxins 1,2,3,6,7,8- and 1,2,3,7,8,9-hexachlorodi-benzodioxin (HCDD) ... 

The total synthesis of the lichen diphenyl ether epiphorellic acid 1 was achieved in the laboratory of J.A. Elix using the Smiles rearrangement as the key step. The diaryl phenolic ester substrate was heated in dry DMSO in the presence of potassium carbonate, which brought about the rearrangement. The resulting carboxylic acid was converted to the methyl ester with diazomethane and was debenzylated under catalytic hydrogenation conditions. 

The newly described depsidones, their occurrence and synthesis are listed in Table 5. The synthesis of depsidones with a lactole ring like those in norstictic, stictic or salazinic acids have caused considerable difficulties. Hareed (353) tried to prepare a depsidone by a) oxidative coupling, b) by a Smiles rearrangement and c) by an Ullmann reaction of a diphenyl ether, but all three attempts failed (see Scheme 123). Some time later Rama (604) successfully synthesized the lactone depsidone 359 and the lactole depsidone 360 via oxidative coupling of a dibenzophenone (see Scheme 124), The structure of the precursor 358... 

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