Kinetics of Reductive N−O Bond Fragmentation:  The Role of a Conical Intersection

Abstract

N-alkoxyheterocycles can act as powerful one-electron acceptors in photochemical electron-transfer reactions. One-electron reduction of these species results in formation of a radical that undergoes N-O bond fragmentation to form an alkoxy radical and a neutral heterocycle. The kinetics of this N-O bond fragmentation reaction have been determined for a series of radicals with varying substituents and extents of delocalization. Rate constants varying over 7 orders of magnitude are obtained. A reaction potential energy surface is described that involves avoidance of a conical intersection. A molecular basis for the variation of the reaction rate constant with radical structure is given in terms of the relationship between the energies of the important molecular orbitals and the reaction potential energy surface. Ab initio and density functional electronic structure calculations provide support for the proposed reaction energy surface.

Enantioselective Direct α-Amination of Aldehydes via a Photoredox Mechanism: A Strategy for Asymmetric Amine Fragment Coupling

“…We postulated that an electrophilic nitrogen-based radical 1 might be generated under mild conditions from an amine substrate 3 that incorporates a photolabile leaving group. While recent literature suggests that nitrogen-centered radicals might be formed using photoredox-active metal complexes, 6 we envisioned that direct access to such open shell reaction partners might be best accomplished using a traceless activation handle such as the dinitrophenylsulfonyloxy group (a subunit that can be chemoselectively triggered using a simple household lightbulb). From the outset, it seemed plausible that an electrophilic nitrogen radical (such as 1 ) would rapidly undergo coupling with a transiently generated π-rich enamine 2 (derived from the condensation of an imidazolidinone catalyst with the aldehyde coupling partner).…”

Development of new dyeing photoinitiators based on 6H-indolo[2,3-b]quinoxaline skeleton

“…(2) Dye photooxidation leading to subsequent polymerization requires molecules that are strong electron acceptors in the ground state. Systems comprised of dyes and N-alkoxyheterocycles acting as one electron acceptors are examples of such systems and photoinitiators for the polymerization of acrylates [2,3].…”

Six‐Membered Heterocycles: Pyridines

“…For example, c-picoline has been condensed with various benzaldehydes to give reasonable yields of heterostilbenes 320 (Scheme 16.108) [235]. Furthermore, treatment of dimethylpyridine 321 with dimethylformamide dimethyl acetal (322) in the presence of catalytic CuI and microwave acceleration at 180 C affords an excellent yield of dienamine 323 [236].…”