Ylides 5-anilinosulfonium

Gassman and co-workers developed a synthetic route from anilines to indoles and oxindoles which involves [2.3]-sigmatropic rearrangement of anilinosul-fonium ylides. These can be prepared from Ai-chloroanilines and ot-thiomcthyl-ketones or from an aniline and a chlorosulfonium salt[l]. The latter sequence is preferable for anilines with ER substituents. Rearrangement and cyclizalion occurs on treatment of the anilinosulfonium salts with EtjN. The initial cyclization product is a 3-(methylthio)indole and these can be desulfurized with Raney nickel. Use of 2-(methylthio)acetaldehyde generates 2,3-unsubstituled indoles after desulfurization[2]. Treatment of 3-methylthioindoles with tri-fiuoroacetic acid/thiosalieylie acid is a possible alternative to Raney nickel for desulfurization[3]. 

A useful method for ortho-alkylation of aromatic amines is based on [2,3]-sigmatropic rearrangement of S-anilinosulfonium ylides. These ylides are generated from anilinosulfonium ions, which can be prepared from iV-chloroanilines and sulfides.289... 

Anilinosulfonium compounds of type 17 can also be used to synthesize indol-2(3. 0 Ones 19 starting from A -chloroanilines and (methylsulfanyl)acetic ester. The (o-aminophenyl)acetic esters 18 obtained via the S-ylide lead to indol-2(3//)-ones 19 after cyclization and reductive desulfurization. 

In the course of this synthesis, the anilinosulfonium salts 53 are deprotonated by Et3N to give sulfonium ylides, which undergo a Sommelet-Hauser rearrangement (situation 54) to the (o-aminobenzyl) ketones 57. Subsequent (spontaneous) cyclization to 3-thiomethyhndoles 56 and reductive desulfurization lead to the 2- (or 1,2-) substituted indoles 55. 

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