Enantioselective Synthesis of Chiral Piperidines via the Stepwise Dearomatization/Borylation of Pyridines

We have developed a novel approach for the synthesis of enantioenriched 3-boryl-tetrahydropyridines via the Cu(I)-catalyzed regio-, diastereo-, and enantioselective protoborylation of 1,2-dihydropyridines, which were obtained by the partial reduction of the pyridine derivatives. This dearomatization/enantioselective borylation stepwise strategy provides facile access to chiral piperidines together with the stereospecific transformation of a stereogenic C–B bond from readily available starting materials. Furthermore, the utility of this method is demonstrated for the concise synthesis of the antidepressant drug (−)-paroxetine. A theoretical study of the reaction mechanism is also described.