Efficient Diastereoselective Three-Component Synthesis of Pipecolic Amides

An efficient Ugi-type three-component reaction (U-3CR) for the synthesis of pipecolic amides is reported. The U-3CR between electronically diverse isocyanides, carboxylic acids and 4-substituted Delta 1-piperideines proceeds in a highly diastereoselective fashion. The Delta 1-piperideines are obtained by NCS-mediated oxidation of the corresponding 4-substituted piperidines, which in turn are generated by an efficient two-step procedure involving the alkylation of 4-picoline and subsequent catalytic hydrogenation of the pyridine ring. We demonstrate the utility of this U-3CR, in combination with the convertible isocyanide 2-bromo-6-isocyanopyridine, in the synthesis of the anticoagulant argatroban.