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

Abstract

Umpolung of pyridine hydroboration was achieved by the reaction between pyridine and diboron(4) with a base and a proton source.

Pyridine-Mediated B–B Bond Activation of (RO)2B–B(OR)2 for Generating Borylpyridine Anions and Pyridine-Stabilized Boryl Radicals as Useful Boryl Reagents in Organic Synthesis

“…By replacing MeOH with MeOD, 4-deuterated dihydropyrazines were obtained in good yields. 23 Template for SYNTHESIS © Thieme Stuttgart • New York 2021-04-20 page 8 of 14…”

Recent Developments in Transition-Metal-Free Functionalization and Derivatization Reactions of Pyridines

“…On the basis of this mechanistic understanding, Jiao and co-workers developed a novel method for the synthesis of 1,4-dihydropyridines (1,4-DHPs) 86. 66 They harnessed a pyridine/diboron(4)/base system to produce an N-boryl pyridyl anion that was quenched in situ by methanol as a proton source (Scheme 44). In this reaction, pyridine substrates with various substitution patterns were tolerated and electron-withdrawing substituents were beneficial.…”

“…1,4-DHPs have been widely used as organic hydride donors, and this method provides a new approach to these useful molecules, most of which are not easily accessible by conventional synthetic methods. 66 Besides protonation, the N-boryl pyridyl anion can also undergo nucleophilic-substitution reactions with alkyl electrophiles. The independently synthesized ate complex 87 undergoes nucleophilic substitution reaction with alkyl bromide 88 to produce 4-alkylated 1,4-DHP derivative 89, further demonstrating the nucleophilic character of the Nboryl pyridyl anion (Scheme 45).…”

Photoinduced metal-free borylation of aryl halides catalysed by an in situ formed donor–acceptor complex

“…Studer 11 developed radical borylation of aryl iodides with bis(catecholato)diboron (B 2 cat 2 ) as the boron source under mild conditions. Recently, Jiao 12 reported the borylation of aryl halides using 4-phenylpyridine as an efficient catalyst and sodium methanolate as a strong base with bis(pinacolato)diboron (B 2 pin 2 ). Different from Jiao's work, Li, 13 Larionov 14 and Lin 15 independently described simple and efficient methods to convert aryl triflates and aryl halides into aryl radicals under UV irradiation or reductive electrophotocatalysis.…”