Metal-free reductive coupling of aliphatic aldehydes/ketones with 4-cyanopyridines: expanded scope and mechanistic studies

Abstract

An efficient and practical bis(pinacolato)diboron (B2pin2) mediated radical-radical cross-coupling of 4-cyanopyridine with aliphatic aldehydes/ketones has been established. The metal-free protocol features simple and mild reaction conditions, excellent functional group tolerance,...

Iodoperfluoroalkylation of unactivated alkenes via pyridine-boryl radical initiated atom-transfer radical addition

“…The combined molecular dynamics and coordinated driving method 17 implemented in the Automated Design of Chemical Reactions Program 18 was applied to locate the structures of all minima and transition states. In our previous study, we had already shown that electron-deficient pyridines can react with B 2 pin 2 to furnish pyridine-ligated boryl radical IM1 , 12 which can react with perfluoroalkyl iodides to afford perfluoroalkyl radicals via a bimolecular homolytic substitution (S H 2) reaction. 14 Therefore, we will focus on the reaction between allylbenzene 1a and the perfluoroalkyl radical in this work.…”

“…We showed before that 4-cyanopyridine/B 2 pin 2 can be used as a pyridine-4-yl equivalent in reductive coupling reactions with carbonyl derivatives. 12 When using 1.2 equivalents of the 4-cyanopyridine/B 2 pin 2 combination, the ATRA reaction furnished iodoperfluoroalkylation product 3a in 42% yield along with a slight amount of perfluoroalkylative pyridylation product 3a′ . Since increasing the ratio of 4-cyanopyridine/B 2 pin 2 caused an increase of the concentration of pyridine-boryl radicals, we attributed the low yield of 3a to the occurrence of the competitive cross-coupling reaction ( IM1 + IM2 → 3a′ ) in the presence of stoichiometric 4-cyanopyridine/B 2 pin 2 (see Fig.…”

“…Our group and other groups have recently demonstrated that diboron(4) compounds, 11 such as bis(pinacolate)diboron (B 2 pin 2 ) and bis(catecholato)diboron (B 2 cat 2 ), exhibit radical reactivities when binding with suitable pyridines. 12,13 In particular, we have disclosed that the pyridine-boryl radical generated from 4-cyanopyridine and B 2 pin 2 can cleave the carbon–iodine bond of perfluoroalkyl iodides to form a perfluoroalkyl radical. 14 Such perfluoroalkyl radicals can add to α-substituted alkenes to form transient carbon-centered radicals, which couple with the persistent pyridine-boryl radicals to produce perfluoroalkylative pyridinylation products (Scheme 1b, left).…”

Recent advances in metal-mediated nitrogen oxyanion reduction using reductively borylated and silylated N-heterocycles

“…40 Some single nitrogen heterocycles that are used for a variety of organic transformations, including pinacol coupling, are strategically substituted pyridines. [71][72][73][74] The single nitrogen heterocycles are generally para-substituted pyridines with an electron withdrawing group, such as CN or CO 2 Me, and react with B 2 pin 2 to form mono-borylated pyridine-based radicals that deliver a single Bpin substituent. The mono-borylated substituted pyridines may operate via a mechanistic pathway distinct from the diborylated N-heterocycles, providing an opportunity for study of single borylation of nitrogen oxyanion ligands.…”

New modified chitosan composites and nanocomposites for different applications

“…Pyridine nucleus and their derivatives are important class of heterocyclic compounds include compounds exhibiting antimicrobial, antihypoxic activity, antiinflammatory, and analgesic [40]. Functionalized pyridines are not only existing in a wide range of bioactive molecules, but also widely used as building blocks that can be transformed into a series of valuable structures in the preparation of ligands and functional materials [41,42].…”