Oxindoles Sommelet-Hauser rearrangement

Another indole/oxindole synthesis achieves the critical ortho-substitution by Sommelet-Hauser rearrangement of an anilinosiilfonium ion intermediate. Use of P-thioketones (G = R, an alkyl group) generates 2-substituted indoles, whereas P-thioesters (G = OR) lead to oxindoles. In each case, a 3-thio substituent must be removed by desulfuri2ation. 

The chlorosulfonium compounds can also be used for the synthesis of oxindoles, the stable tautomeric form of 2-hydroxyindoles. The a -methylthio ketone is replaced by ethyl methylthioacetate and the products of the Sommelet-Hauser rearrangement are cyclized to 3-methylthiooxindoles. The methylthiooxindoles are reductively desulfurized with Raney nickel (equation 102) (74JA5508). 

In 1981, Wierenga first introduced a modification of Gassman oxindole synthesis for the synthesis of indole derivative 34, part of the left-hand segment of the antitumor agent CC-1065. In accordance to that, addition of derivative 30 in a equimolar amount of the hindered base, [1,8-bis(dimethylamino)naphthylene (R3N), to the chloride complex of ethyl-a-(mercaptomethyl)propionate 31, followed by a triethylamine catalyzed Sommelet-Hauser rearrangement and an acid-induced cyclization gave oxindole 32. Treatment of 32 with excess BH3 SMei at room temperature afforded 33 in 95% yield. 

Catalytic thia-Sommelet-Hauser rearrangement toward the synthesis of oxindoles... 

A series of 3-arylthio-l,3-disubstituted-oxindoles were prepared by the reaction of a-diazocarbonyl compounds and sulfenamides involving a Rh-catalysed thia-Sommelet-Hauser-type rearrangement (Scheme 100). (g)... 

Further reaction of A -chloroaniline 6 with ethyl (methyl)thioacetate yields azasulfonium ion 7, which forms ylide 8 upon deprotonation with triethylamine. After the ylide undergoes a [2,3]-Sommelet-Hauser-like rearrangement, a proton transfer and subsequent rearomatization produces the intermediate aniline derivative 9, which upon cyclization forms a transient tetrahedral anion. Collapse of the anion with loss of ethoxide produces the stable oxindole derivative 2. Removal of the methyl thiol functionality with Raney nickel produces the final product 3. 

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