Rediscovering the Chemistry of Sulfur Dioxide: New Developments in Synthesis and Catalysis

Abstract

The recent development of several sulfur dioxide surrogates has seen a renaissance in its chemistry, with a number of new synthetic methods being reported. This article reviews the reactions of sulfur dioxide and sulfur dioxide surrogates, with an emphasis on recent examples.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

“…Despite, or perhaps as a result of this rich history, the chemistry of sulfinate salts has enjoyed a renaissance in the past 10 years, predominantly as a result of the development of SO 2 surrogates: bench stable, crystalline compounds that can either release SO 2 in situ or react directly as SO 2 equivalents (Scheme 150). 457,458 Predominant among these new reagents are DABSO 459,460 (a charge transfer complex between DABCO and two molecules of SO 2 ) and inorganic sulfur containing salts (e.g., potassium metabisulfite 461 and sodium sulfite 462 ). As this field is so broad, with new developments reported with an astonishing regularity, it is beyond the scope of this section to conduct an exhaustive review.…”

Three‐Component C–H Bond Sulfonylation of Imidazoheterocycles by Visible‐Light Organophotoredox Catalysis

“…[ 7,8 ] The importance of this approach relies on the development of bench‐stable and easy handled SO 2 surrogates which circumvent the toxicity and the drawbacks associated with handling gaseous sulfur dioxide. [ 9 ] In the omnipresent field of C–H bond functionalization, sulfonylation has also become a subject of significant work with achievements made using one sulfur partner often sulfonates or sulfonyl halides. [ 10 ] In contrast, combining C–H bond sulfonylation and direct incorporation of SO 2 in a three‐component approach still remains rare despite its advantage in terms of atom‐economy and convergence.…”

“…Initially, we screened various ruthenium and iridium polypyridyl complexes or organic dyes as photoredox catalysts and solvents, using 2‐phenylimidazo[1,2‐ a ]pyridine 1 and a phenyl diazonium salt as coupling partners in the presence of 1,4‐diazabicyclo[2.2.2]octane bis (sulfur dioxide) adduct [DABCO · (SO 2 ) 2 ] as sulfur source, popularized by Willis et al, under light irradiation at room temperature (not shown). [ 9a,9b ] In the best case scenario, only traces of the expected sulfonylated compound 3 was observed. Instead, the diazenylimidazo[1,2‐ a ]pyridine 4 was isolated as the major product in an average yield of 70 %.…”

“…Inorganic sulfite salts are also well‐developed sources for delivery sulfur dioxide. [ 9c,9d ] When DABCO · (SO 2 ) 2 was replaced with sodium metabisulfite Na 2 S 2 O 5 , the yield of the sulfonylation process dropped to 31 % probably due to solubility issues (entry 13). Surprisingly, DMSO proved to be the only effective solvent as reaction in other polar solvents such as DMF, CH 3 CN, MeOH, dioxane and in THF and CH 2 Cl 2 resulted in no conversion.…”

Visible-Light-Induced Trifluoromethylsulfonylation Reaction of Diazo Compounds Enabled by Manganese Catalysis

“…On the other hand, sulfones, as a common class of compounds, play an important role in the synthesis of molecular drugs and agrochemicals as well as in various organic transformations . Several general strategies have been devoted to the synthesis of functionalized sulfones, including oxidation of sulfides, transfer of sulfonyl precursors, and three-component reaction of SO 2 or SO 2 surrogates (Scheme a), but these methods involve safety issues and limitations of application caused by the use of strong oxidants or highly toxic and corrosive SO 2 . Considering the broad utility of trifluoromethyl sulfones in chemistry as well as the high reactivity of carbene species, we are interested in using carbenes as acceptors to capture trifluoromethyl sulfone radicals.…”