The photochemical alkylation and reduction of heteroarenes

Abstract

The functionalization of heteroarenes has been integral to the structural diversification of medicinally active molecules such as quinolines, pyridines, and phenanthridines.

Birch‐Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer

“…[13][14][15] Photochemical arene reductions are well known, however,because of the absorption properties and high stabilities of arenes,U Vl ight-initiated reactions in the presence of super-stoichiometric amounts of strong reducing agents are required. [16][17][18][19] Despite many applications of visible-light photocatalysis in organic synthesis, [20,21] ad irect reduction of aromatic compounds has not been achieved using visible-light photoredox catalysis.One reason for this is that the energy of blue (455 nm) and green photons (530 nm) of 2.72 eV and 2.34 eV,r espectively,a re insufficient for most arenes to overcome the inherent aromatic stabilization that allows dearomatization. Alternatively,e nergy accumulation from more than one photon may open ap ath for visible-lightmediated dearomatization of stable arenes.…”

Recent Advances in Methylation: A Guide for Selecting Methylation Reagents

“…Instead of TFA, HCl was used as the additive for the protonation of substrates. As a comparison, 72 ( b ) was obtained in 80 % yield …”

“…It can be used as a guide for chemists wanting to apply the best methylation conditions in their work. Despite the fact that only methylation chemistry is covered in this review, certain methods also work well for accessing other alkyl groups, such as cyclic (cyclopropyl, ‐pentyl, and ‐hexyl) alkyl groups, benzylation, etc …”

“…As ac omparison, 72(b)w as obtained in 80 %y ield. [45] Considering this recent success, Ib elieve that these metalfree photoinduced alkylations will inspire chemists to explore appropriate metal-free conditions to generate hydroxymethyl radicals (CCH 2 OH), and design reactions towards additional aromatic systems commonly used in the chemistry community.…”

Jenseits von Friedel und Crafts: immanente Alkylierung von C‐H‐Bindungen in Arenen

“…Alkohole wurden auch von Barriault für die photochemische Alkylierung einiger Chinoline und Pyridine in Gegenwart konzentrierter HCl unter Bestrahlung mit UVA‐Licht umgesetzt, von Liu für die metallfreie photochemische Methylierung von N‐Heteroarenen mit Methanol, von Ghosh für die übergangsmetallfreie Alkylierung von C8‐substituierten Chinolin‐ N ‐oxiden mit sekundären und tertiären Alkoholen über eine oxidative Alkylverschiebung und von Zhang für die wasserstofftransfervermittelte β‐Alkylierung von Aryl‐1,8‐naphthyridinen, zumeist mit Benzylalkoholen, unter metallfreien Bedingungen …”