David E. Herbert

Direct Electrochemical Hydrogenation of C=N and C=O Bonds in

Acidic Solution

Dihydropyridines (DHPs) are biologically active structures and a useful

class of organohydride donors that mimic the nicotinamide sub-unit of NAD(P)H.

Similar to the effect of carbonyl substituents in Hantzsch esters, benzannulation

of pyridines can both impact the ease of DHP formation and their hydricity once

formed. For example, 1,2-dihydrophenanthridine, the DHP of

phenanthridine (3,4-benzoquinoline) is a competent hydride donor that can be

generated catalytically and used in tandem with chiral Brønsted acids in the

(catalytic) enantioselective reduction of C=O and C=N bonds.[1] In these cases,

H2 at pressure and transition metal catalysts or additives were required to

(re)generate the DHP. The potential to replace fossil-derived H2 or traditional

hydride reagents with protons (H+) and a renewable source of electrons (e-) in

hydrogenation reactions and organic reductions is an appealing target in

sustainable chemistry. In this presentation, I will discuss our development of an

electrochemical approach[2] to the hydrogenation of a benzannulated pyridine,

phenanthridine, to a DHP 1,2-dihydrophenanthridine, as well as the broader

extension of this chemistry in the hydrogenation of C=N and C=O bonds and

applications in electrochemical reduction CO2.[3]