Palladium-Catalyzed Three-Component Diaryl Sulfone Synthesis Exploiting the Sulfur Dioxide Surrogate DABSO**

play novel properties as materials. Although there are a variety of methods known for the preparation of sulfones, the majority of these processes feature associated limitations. For example, oxidation of the corresponding sulfide relies on functional-group compatibility with oxidizing agents and the availability of catalysts to promote selectivity for sulfone formation over sulfoxide formation; in addition, the preparation of the required sulfide substrate often involves the use of foul-smelling thiols. Friedel–Crafts-type sulfonylation of arenes is limited not only by the generally harsh reaction conditions, but also by the inherent regioselective bias imposed by the electronic and steric properties of the arene substrate. In response to these limitations, the use of transitionmetal-catalyzed cross-coupling has been exploited as a route to sulfones. The most utilized has been copper catalysis, in which sodium sulfinates couple with aryl, heteroaryl, or alkenyl halides, or boronic acids. However, the requirement for stoichiometric phase-transfer additives, high temperatures, and the use of undesirable solvents or ionic liquids, are significant drawbacks. An analogous palladium-catalyzed approach has also been developed using (pseudo)halides as coupling partners, although it too features the use of stoichiometric additives and high temperatures, and consequently suffers from limited scope. In addition to these problems, the variety of sulfones prepared by these metalcatalyzed methods is poor; only a small number of sodium sulfinates (typically methyl, phenyl, and p-tolyl) have been used to demonstrate the scope. This reflects the very limited commercial availability of sodium sulfinates, perhaps as a result of impractical or limited synthetic routes. Organometallic addition to sulfur dioxide gas (followed by cation exchange) and reduction of the sulfonyl chloride are two such examples, but both have shortcomings such as the harsh conditions associated with sulfonyl chloride formation or the use of toxic gaseous sulfur dioxide. Taken together, these limitations present a clear mandate for the development of a more general, modular synthesis of sulfones, with the versatility to allow ready variation of both groups attached to the SO2 linker. [14] We have recently developed DABSO (1), which is a solid, bench-stable complex formed between 1,4-diazabicyclo[2.2.2]octane (DABCO) and two sulfur dioxide molecules, as an easy-to-handle surrogate for sulfur dioxide gas (Scheme 2). We have demonstrated its use in known reactions