Mild, Fast, and Easy To Conduct MoCl₅-Mediated Dehydrogenative Coupling Reactions in Flow

Abstract

A convenient and straightforward approach to performing oxidative coupling reactions in flow is presented. A collection of electron-rich benzene derivatives was subjected to this protocol, and the distinct utility of molybdenum pentachloride (MoCl) is established. Using this unexplored protocol, biphenyls could be obtained in 21-91% isolated yield. This simple protocol opens a new chapter in reagent-mediated dehydrogenative coupling reactions, and yields are compared to classical approaches.

Carbocatalytic Oxidative Dehydrogenative Couplings of (Hetero)Aryls by Oxidized Multi‐Walled Carbon Nanotubes in Liquid Phase

“…We selected HNO 3 ‐oxidized multi‐walled (MW)CNTs out of the several reported materials for catalysis testing as the oxidation procedure is well‐studied including the spectroscopic and thermogravimetric analysis of produced functional groups on the MWCNTs . For the test reaction of catalysis we selected dimerization of 1 a (Table ) to 2 a as it is one of the prototypical ODH‐reactions that has been studied with different oxidative systems such as DDQ/H + , PIFA, MoCl 5 , NaNO 2 /H + , electrolysis, FeCl 3 /SiO 2 , and MnO 2 /BF 3 ⋅OEt 2 …”

“…We selected HNO 3 -oxidized multi-walled (MW)CNTso ut of the several reported materials [21] for catalysis testing as the oxidation procedure is well-studied including the spectroscopic and thermogravimetric analysis of produced functional groups on the MWCNTs. [22,23] For the test reaction of catalysis we selected dimerizationof1a (Table 1) to 2a as it is one of the prototypical ODH-reactionst hat has been studied with different oxidative systems such as DDQ/H + , [24] PIFA, [25] MoCl 5 , [26] NaNO 2 / H + , [27] electrolysis, [28] FeCl 3 /SiO 2 , [29] and MnO 2 /BF 3 •OEt 2 . [30] Using toluene as solvent, we screened several variables such as temperature, molarity,r eactiont ime, loading of catalyst, and the amount of MsOH additive (see the Supporting Information (SI)), which is knownt oi ncreaseo xidationp otentialo fm olecular quinones.…”

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…Molybdenum pentachloride is as elective,o ne-electron oxidizing reagent frequently employed in many batch oxidative coupling processes, [12] and more recently under continuous-flow conditions. [13] In most MoCl 5 -mediated reactions of this type,undesired chlorination can be successfully avoided, as the CÀCcoupling is much faster than other side reactions. However,f or highly electron-rich substrates or when the coupling process proceeds slowly,c hlorination becomes an issue.…”

Rhodaelectro-Catalyzed C–H and C–C Activation

“…90 It is particularly noteworthy that C−H/N−H alkyne annulations were amenable to electroflow technology using a slightly modified IKA setup. [91][92][93][94][95][96][97][98] This strategy represents a user-friendly tool for the efficient upscaling of a reaction with significantly improved control of heat and mass transfer. The scope for this challenging flow rhodaelectro-catalyzed alkyne annulation gave access to isoquinolines, as well as azo-tetracycles, by an intramolecular reaction.…”