| 摘要 |
Methodologies for the alpha-monohalogenation of acid sensitive ketones, especially cyclic, acid-sensitive, ketalized ketones. As one approach, the ketone is reacted with a halogen donor compound, e.g., N-chlorosuccinimide, in anhydrous, highly polar organic reagents such as dimethylformamide (DMF). As another monohalogenation approach, it has been observed that organic salts generated from amines and carboxylic acids catalyze the monohalogenation of ketalized ketone in reagents comprising alcohol solvent (methanol, ethanol, isopropanol, etc.). The monohalogenation is fast even at -5° C. The salt can be rapidly formed in situ from ingredients including amines and/or carboxylic acids without undue degradation of the acid sensitive ketal. Aryl ketones are monooxygenated using iodosylbenzene. This methodology is applied to monohalogenation of an acid sensitive monoketal ketone. The ability to prepare monohalogenated, acid sensitive ketones facilitates syntheses using halogenated, acid sensitive ketones. As just one example, facile synthesis of halogenated, acid sensitive ketones provides a new approach to synthesize the S-ketal-acid S-MBA (S-methylbenzylamine) salt useful as an intermediate in the manufacture of a glucokinase activator. As an overview of this scheme, a monohalogenated, cyclic, ketalized ketone is prepared using monohalogenation methodologies of the present invention. The halogenated compound is then subjected to a Favorskii rearrangement under conditions to provide the racemic acid counterpart of the desired chiral salt. The desired chiral salt is readily recovered in enantiomerically pure form from the racemic mixture.
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