Potassium Phosphate-Catalyzed Chemoselective Reduction of α-Keto Amides: Route to Synthesize Passerini Adducts and 3-Phenyloxindoles

A chemoselective reduction of α-keto amides to biologically important α-hydroxy amides (mandelamides) by polymethylhydrosiloxane (PMHS) using 5 mol% potassium phosphate (K3PO4) as catalyst has been developed. This transition metal-free protocol discloses excellent chemoselectivity for the ketone reduction of α-keto amides in the presence of other reducible functionalities like ketone, nitro, halides, nitrile and amide. Also, the chemoselectively reduced α-hydroxy amide has been derivatized to isocyanide-free Passerini adducts. The N-alkyl-α-hydroxy amides have been successfully converted to 3-phenyloxindole derivatives by treatment with methanesulfonyl cholride and triethylamine.