Abstract
The combination of 1-benzyl-1,4-dihydropyridines with the strong Lewis acid, B(C6F5)3, generates a stable pyridinium borohydride species in high yields (94%) in as little as 10 min. This use of biologically inspired hydride sources further builds on the recent work of new hydride donors in the formation of borohydrides. When functionalizing the dihydropyridine with an amide or carboxylic acid moiety, a disproportionation reaction composed of a series of protonation/reduction steps is observed upon the addition of B(C6F5)3. As a result, one equivalent of dihydropyridine undergoes net hydrogenation, whereas the other is dehydrogenated yielding the pyridinium counterpart in a transfer hydrogenation-type mechanism.This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.
Highlights
In recent years, the field of frustrated Lewis pairs has seen vast developments in a number of applications as a way of inducing alternative reactivity, sometimes counter to what is the ‘traditional’ pathway of Lewis acid/base reactions [1]
This work has built upon an area of main group chemistry that has yet to be fully explored, the generation of borohydrides from biologically inspired sources
It has been shown that the combination of the strong Lewis acid, B(C6F5)3, and unactivated dihydropyridines result in a thermally stable borohydride through hydride abstraction
Summary
The field of frustrated Lewis pairs has seen vast developments in a number of applications as a way of inducing alternative reactivity, sometimes counter to what is the ‘traditional’ pathway of Lewis acid/base reactions [1]. While mixtures of conventional Lewis acids and Lewis bases result in adduct formation, which is a ubiquitous motif in organic and organometallic chemistry, a frustrated system is achieved when the steric bulk about the lone pair donor and acceptor is increased, precluding adduct formation. The development of frustrated Lewis pairs has led to great advancements in small molecule activation, in molecular.
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