Hindered Hauser bases

The magnesium amides of choice for the preparation of magnesium enolates via met-allation are the Hauser bases, such as 39 and 40, or (bis)amidomagnesium reagents, such as 46 and 47. The reaction has been successfully applied to the preparation of enolates derived from cyclic, acyclic and a-siloxyketones, benzyUc ketones, aldehydes, carboxylic esters and amides, even with the less hindered Hauser bases. 

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. 

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