Bromination of α‐Diazo Phenylacetate Derivatives Using Cobalt(II) Bromide

Abstract

A method for the bromination of α‐diazo phenylacetate derivatives using cobalt(II) bromide is described. This bromination reaction features a short reaction time, broad substrate scope, operational simplicity, acid‐free conditions, and gram‐scalability.magnified image

Visible‐Light‐Induced Bromination of α‐Diazo Compounds with Bromoform

“…[5] More recently, the Gu group reported the cobalt-mediated bromination of α-diazo phenylacetate derivatives protocol (Scheme 1c). [6] This protocol suffered from high temperature and the use of stoichiometric cobalt (II) bromide, which may cause incompatibility of functional groups, serious waste, and pollution. Therefore, a green and practical protocol for the synthesis of α-brominated phenylacetate derivatives remained to be desirable.…”

“…However, the bromination of α ‐diazo compounds relied on the employment of elemental bromine or hydrogen bromide (Scheme 1a and 1b), and the strong acidity, toxic and hazardous nature of these reagents limit their applications [5] . More recently, the Gu group reported the cobalt‐mediated bromination of α‐diazo phenylacetate derivatives protocol (Scheme 1c) [6] . This protocol suffered from high temperature and the use of stoichiometric cobalt (II) bromide, which may cause incompatibility of functional groups, serious waste, and pollution.…”

TfOH-catalyzed regioselective N2-alkylation of indazoles with diazo compounds

“…Here we describe a strategy for N 2 -alkylation of indazoles via metal-free reactions with diazo compounds under TfOH catalysis, allowing for the controllable regioselective N 2 -alkylation of indazole from diazo compounds in high yield with excellent functional group tolerance (Scheme 2, D). [24][25][26] The reaction mechanism and the origin of the intriguing chemoselectivity of the reaction were rationalized by controlled experiments.…”