Abstract
The oxidative coupling of secondary aldehydes and sulfinate salts is achieved using copper catalysis to form α-sulfonyl aldehydes. The use of an acidic co-solvent is important to adjust the oxidation potential of MnO2 as an oxidant. A broad range of sulfonylated aldehydes is prepared, and their further functionalisation is demonstrated. A dual ionic/radical pathway mechanism is proposed.
Highlights
The oxidative coupling of secondary aldehydes and sulfinate salts is achieved using copper catalysis to form a-sulfonyl aldehydes
Sulfinate salts are attractive nucleophiles to use in oxidative couplings as readily available, handled solids, for the direct preparation of medicinally important sulfones,[2] but can themselves be oxidised in an unproductive manner. a-Quaternary sulfones feature in several medicinally relevant compounds (Fig. 1b).[3,4,5,6]
There are few direct methods used for their synthesis and current routes require multiple steps: thioalkylation oxidation, double alkylation of a sulfonyl ester/nitrile, reaction of a pre-formed enolate with a sulfonyl fluoride under cryogenic conditions,[3,4,5,6] rearrangement of vinyl tosylates,[7] or rearrangement of an epoxysulfone.[8]
Summary
The oxidative coupling of secondary aldehydes and sulfinate salts is achieved using copper catalysis to form a-sulfonyl aldehydes. Sulfinate salts are attractive nucleophiles to use in oxidative couplings as readily available, handled solids, for the direct preparation of medicinally important sulfones,[2] but can themselves be oxidised in an unproductive manner. Effective conditions for the coupling of cyclohexane carboxaldehyde 1 with p-tolylSO2Na 2a were achieved using the combination of copper triflate with bathophenanthroline ligand, and silver acetate (Scheme 1a).
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