Activation of DMSO for Swern-type oxidation by 1,1-dichlorocycloheptatriene

Abstract

The oxidation of alcohols to their corresponding carbonyl compounds is a frequently employed fundamental organic transformation in synthetic laboratories and the chemical industry. 1 One of the most historic and widely used methods for alcohol oxidation involves the activation of dimethylsulfoxide (DMSO) by a variety of electrophilic reagents such as oxalyl chloride (Swern oxidation), dicyclohexylcarbodiimide (Pfitzner-Moffat), SO 3 .pyridine (Parikh-Doering), trifluoroacetic acid anhydride (Omura-Sharma-Swern) and N-chlorosuccinimide (Corey-Kim oxidation with dialkyl sulfide). 2 Among these DMSO-activation methods, Swern oxidation has regularly been the default pathway due to its consistent efficiency over a broad range of substrates. 2 The original Swern oxidation employed oxalyl chloride to form the reactive chlorodimethylsulfonium chloride, which subsequently reacted with alcohols and bases to give the carbonyl compounds and dimethyl sulfide. 3 The activation of DMSO by oxalyl chloride is strongly exothermic and violently generates toxic gases such that it has to be carried out at very low temperature in a well-ventilated area. 2-4 Furthermore, oxalyl chloride itself is a volatile toxic reagent that can be difficult to handle. There have been several studies investigating other chloride-bearing reagents for the replacement of oxalyl chloride in Swern-type oxidation reactions, most notably cyanuric chloride 4 and triphenylphosphine dichloride. 1 These reagents consist of reactive chlorides bonding to a heterocycle (cyanuric six-membered ring) or heteroatom (phosphorus in phosphine dichloride). Herein, we report the use of 1,1-dichlorocycloheptatriene (1) (Scheme 1), a simple chlorinated hydrocarbon, as a new DMSO activator for efficient Swern-type oxidation of a broad range of alcohol substrates under mild reaction conditions.

The Ambivalent Nature of Halogenated Tropone Derivatives: Dihalocycloheptatriene vs. Halotropylium Halide

“…[5,6] The solid-state structure of 2 pointed out that halotropylium ions can serve as halogenbond donors. These isomers can interconvert through halide expulsion and subsequent attack on a different position of the intermediate halotropylium ion.…”

“…[1] In recent years, both these compounds have found synthetic use as precursors for carbocyclic carbene complexes. [5,6] It is therefore somewhat surprising that the solid-state structures of 1 and 2 have never been elucidated. [5,6] It is therefore somewhat surprising that the solid-state structures of 1 and 2 have never been elucidated.…”

“…[1,7] Ion pairs vs. covalently bound halogens have also been discussed both as stable and transient species in some other cases. [2][3][4][5][6] The active species in the applications of 1, however, is considered to be the chlorotropylium ion (see A for X = Cl). [2][3][4][5][6] The active species in the applications of 1, however, is considered to be the chlorotropylium ion (see A for X = Cl).…”

“…[8] Despite the early contrary findings, B became the most widely used representation of 1 and 2 in recent literature. [5,6] As the structure has consequences for the mechanistic understanding of the reactivity of 1 and 2, we want to clarify the nature of these compounds in this publication. [5,6] As the structure has consequences for the mechanistic understanding of the reactivity of 1 and 2, we want to clarify the nature of these compounds in this publication.…”

Promotion of Organic Reactions by Non‐Benzenoid Carbocyclic Aromatic Ions

“…[24] Ther eaction between 40 and DMSO (46) afforded sulfonium intermediate 47 and tropone (4)a sab yproduct. [24] Ther eaction between 40 and DMSO (46) afforded sulfonium intermediate 47 and tropone (4)a sab yproduct.…”