Manganese‐Catalyzed Aerobic Heterocoupling of Aryl Grignard Reagents

Abstract

An improved protocol has been developed for the MnCl2-catalyzed cross coupling of two arylmagnesium bromides under an atmosphere of dioxygen. The reaction is achieved with a 2:1 ratio between the Grignard reagents and 20% of MnCl2. Very good yields of the heterocoupling product can be obtained when the limiting Grignard regent undergoes very little homocoupling under the reaction conditions. Arylmagnesium bromides with p-methoxy, pdimethylamino, p-fluoro and p-chloro substituents were shown to give high yields in the cross coupling with a variety of substituted aryl Grignard reagents. Heterocyclic Grignard reagents, on the other hand, were less effective substrates for the transformation due to a rapid homocoupling with these reagents.

Carbazole‐Based N‐Heterocyclic Carbenes for the Promotion of Copper‐Catalyzed Palladium‐Free Homo‐/Hetero‐Coupling of Alkynes and Sonogashira Reactions

“…Unsymmetrical diynes‐via heterocoupling of two different alkynes is a synthetic challenge that could be undertaken in a similar manner to that involving the heterocoupling of Grignard reagents, Zinc reagents, boronic acids . An efficient way to promote the hetero‐coupling‐vs homo‐coupling is to employ electronically distinct alkynes (i. e. electron‐withdrawing and electron‐donating substituents bearing alkynes) which modulates the electronic factors on the catalytically active metal center providing the hetero‐coupled product preferentially over the homo‐coupled one.…”

Manganese‐Catalyzed Cross‐Coupling Processes

“…In 2017, Madsen further examined this heterocoupling reaction of aryl Grignard reagents by lowering the catalyst loading (20 mol% with respect to the default reagent), using a 2:1 ratio between the coupling partners and decreasing the temperature to -10 °C [33]. Under these conditions, Grignard reagents having p-OMe, p-NMe2, p-F or p-Cl substituted aryl groups afforded no or only very small amounts of homocoupling byproduct.…”

Transition-Metal-Catalyzed Cross-Coupling Reactions of Grignard Reagents

“…161 Mn-catalyzed oxidative cross-coupling was further developed by Madsen and co-workers, who, in 2017, reported the coupling of two arylmagnesium bromides under oxygen in the presence of MnCl 2 . 162 In 2017, Madsen and co-workers reported the MnCl 2catalyzed cross-coupling reaction of Grignard reagents with aryl halides. 163 The reaction is limited to aryl chlorides containing a cyano or an ester group in the para position or a cyano group in the ortho position.…”