Metal‐ and Reagent‐Free Electrochemical Synthesis of Alkyl Arylsulfonates in a Multi‐Component Reaction

Abstract

This work presents the first electrochemical preparation of alkyl arylsulfonates by direct anodic oxidation of electron‐rich arenes. The reaction mechanism features a multi‐component reaction consisting of electron‐rich arenes, an alcohol of choice and excess SO 2 in an acetonitrile‐HFIP reaction mixture. In‐situ formed monoalkyl sulfites are considered as key intermediates with bifunctional purpose. Firstly, this species functions as nucleophile and secondly, excellent conductivity is provided. Several primary and secondary alcohols and electron‐rich arenes are implemented in this reaction to form the alkyl arylsulfonates in yields up to 73 % with exquisite selectivity. Boron‐doped diamond electrodes (BDD) are employed in divided cells, separated by a simple commercially available glass frit.

Metal‐Free Electrochemical Synthesis of Sulfonamides Directly from (Hetero)arenes, SO2, and Amines

“…Guided by our previous studies on arylsulfonates, [28] we chose 1,2,3‐trimethoxybenzene as arene model substrate for reaction optimization in combination with morpholine as amine. We were delighted to observe the formation of the desired sulfonamide as two regioisomers 5 a and 5 b in a 6:1 ratio as depicted in Scheme 3.…”

“…Harsh reaction conditions and multiple equivalents [26] of the corrosive chlorosulfuric acid are often required and the selectivity is limited to the inherent reactivity of the aromatic compound, which can result in regioisomer mixtures. [27,28] An interesting alternative method was reported by Willis and co-workers featuring the Cu II -catalyzed synthesis of sulfonamides starting from the corresponding arylboronic acid with DABSO as SO 2 source. [6] However, harsh reaction conditions, the cost of DABSO, necessary prefunctionalization of the arene and excess of the boronic acid component are drawbacks in this approach.…”

Metallfreie, elektrochemische Synthese von Sulfonamiden direkt aus (Hetero)arenen, SO2 und Aminen

“…Oft sind drastische Reaktionsbedingungen und mehrere Äquivalente [26] der korrosiven Chlorschwefelsäure erforderlich. Darüber hinaus ist die Selektivität auf die inhärente Reaktivität der aromatischen Verbindung beschränkt, was zu Regioisomeren‐Gemischen führen kann [27, 28] . Eine interessante Alternative wurde von Willis und Mitarbeitern mit der Cu II ‐katalysierten Synthese von Sulfonamiden ausgehend von der entsprechenden Arylboronsäure mit DABSO als SO 2 ‐Quelle publiziert [6] .…”

“…Darüber hinaus machen die Robustheit solcher Transformationen [39] und die lange Lebensdauer von BDD‐Elektroden [40] in Kombination mit der Möglichkeit der HFIP‐Rückgewinnung [35, 41] diesen Ansatz noch umweltfreundlicher. Erst kürzlich publizierte unsere Gruppe die elektrochemische Synthese von Alkylarylsulfonaten aus Arenen, Alkoholen und SO 2 in einer Mehrkomponentenreaktion [28] . Dies ermutigte uns, die direkte elektrochemische Synthese von Sulfonamiden zu erforschen.…”

Electrosynthesis 2.0 in 1,1,1,3,3,3‐Hexafluoroisopropanol/Amine Mixtures

“…BDD electrodes are employed in divided cells at galvanostatic conditions, separated by a simple commercially available glass frit. [61]…”