An umpolung approach to the hydroboration of pyridines: a novel and efficient synthesis of -H 1,4-dihydropyridines.

The first inverse hydroboration of pyridine with a diboron(4) compound and a proton source has been realized under simple basic and catalyst-free conditions. This process consists of a formal boryl anion addition to pyridine, which produces an -boryl pyridyl anion complex, and the subsequent protonation of the anion complex. This process enables a simple and efficient method for the synthesis of multi-substituted -H 1,4-dihydropyridine (1,4-DHP) derivatives that are difficult to prepare using established methods. Furthermore, this method allows for facile preparation of 4-deuterated 1,4-DHPs from an easily accessible deuterium ion source. This inverse hydroboration reaction represents a new mode for pyridine functionalization.