Stereocontrolled entry to borylated piperidines via stepwise dearomative carboboration of pyridines

We disclose a stepwise dearomative carboboration that converts pyridine precursors into substituted borylated piperidines with excellent site-, regio-, and diastereocontrol. In this strategy, pyridines are first converted to 1,2-dihydropyridines by regioselective nucleophilic dearomatization, and the resulting dihydropyridines undergo Pd-catalyzed carboboration with diverse alkenyl triflates and diboron reagents. Computational analysis supports a non-classical activation mode of diboron that involves oxidative addition to palladium to access a transient Pd(iv) intermediate and identifies the features that control selectivity. Downstream derivatizations of the boronate handle highlight the synthetic versatility of the products.