Aryl sulfonates arenes

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

D. Arene Sulfonate-Aryl Sulfone (Sulfone-Fries) Rearrangement71... 

Polysulfonates can also be obtained using the condensation reaction of aryl sulfonic acids with arenes [Eq. (45)] [134],... 

By treatment with HSOsF-SbFs (1 1) and sulfur dioxide, alkylbenzenes, haloben-zenes, and alkylhalobenzenes are converted to their corresponding diaryl sulfoxides along with small amounts of diaryl sulfides as minor products (Eq. 35) [81]. In the absence of SO2 aryl sulfone formation is the dominant process, although sulfoxide is also formed. Unsymmetrical (mixed) sulfoxides can be prepared by adding one molar equivalent of an arene to the solution of the second arene and magic acid-SOa in Freon at low temperatures. 

Oxidative Pd insertion into electron-poor aryl sulfonates is a key step in Pd(0)-mediated C-C coupling reactions. This principle has been turned into a traceless linker concept in which phenols are attached via sulfonates to a solid support [107]. The system has been optimized by employing a perfluoroalkylsulfonyl linker that closely resembles the commonly applied inflates (90, Scheme 41). In this respect, the linker acts as a protecting group and as an activating entity. Reductive cleavage of 91 with Pd(0) and formic acid led to arenes 92 [108]. 

A number of other types of calixarene esters are known, including the aryl-sulfonates (often used to establish the calix[4]arenes in the cone conforma-tion ), phosphates (often used as intermediates in the replacement of the OH groups with and phosphonates. ... 

The reagents (R = CH3, C2HS) react with activated arenes without Friedel-Crafts catalysts to form alkyl aryl sulfones. Alkylation rather than sulfonylation is observed when R = CH(CH3)2. Sulfonylation involves the sulfonylium ion RSO2 when R is a secondary alkyl group the ion readily loses SO2 to give the carbonium ion. ... 

VNS is also of general character in respect to electron-deficient arenes. Nitrobenzene, the model representative of these arenes, can enter into VNS with any carbanion presented earlier. The reaction of nitrobenzene with secondary carbanions such as chloromethyl aryl sulfones or aryloxyacetoni-triles can proceed at positions ortho and para the orientation is controlled by the conditions. At low temperature and excess of strong base (kinetic control), ortho substitution dominates, whereas thermodynamic control favors para substitution (Scheme 11.23) [42]. The reaction proceeds mainly in the ortho position also when carried out in r-BuOK/THF system due to specific solvation effect [38]. StericaUy demanding tertiary carbanions, RcH, react preferentially in para positions. 

These reactions are typically promoted by metal catalysts. While ortho-directing groups have promoted the formation of ortho-substituted arenes using palladium catalysts [68], ruthenium complexes have been shown to generate the meta-substituted aryl sulfone using the same ortho-directing group [67]... 

Progress has been made in extending the Suzuki reaction from aryl triflates, to other less reactive aryl sulfonates, which show poor reactivity towards oxidative addition to Pd(0). A recent approach to this problem involves the activation of 1 triflates by complexation of electron-withdrawing Cr(CO)3 to the arene moiety (144). 

The relative ease with which aryl benzyl sulfoxides undergo homolytic dissociation (Rayner et al., 1966) as compared to aryl benzyl sulfides or sulfones is supportive of this idea that ArSO radicals are easier to form than ArS or ArS02 radicals. Another interesting set of observations is the following. Booms and Cram (1972) found that optically active arene-sulfinamides ArS(0)NRPh (R = H or CH3) racemize thermally very readily at room temperature and that this racemization is the result of a free radical chain reaction (160) that is initiated by the dissociation of some of the sulfinamide into an ArSO and a PhNR radical (159). While the length of the inhibition... 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

The sulfonated calix[8]arene 27 (Structures 8), which can be viewed as a simplified y-CD with the carbohydrate backbone replaced by an aryl moiety, mimicked heparin in the stimulation of heparan sulfate synthesis from cultured endothelial cells [62]. 

The DBU/bis(trimethylsilyl)acetamide (BTMSA) double condensation of nitro(hetero)arenes with cinnamyl-based sulfones yields 2-aryl-4-arylsulfonyl heterocycles in good to excellent yields (DBU= l,8-diazabicyclo[5.4.0]-undec-7-ene Scheme 33) <1997TL4913, 1998T2607>. 

Due to the relatively slow addition of aryl radicals to substituted benzenes [7], inter-molecular Gomberg-Bachmann type arylations often require favorable reaction conditions in which the substrate arene is used as solvent to be efficient. To achieve good control and selectivity in the addition step, radical biphenyl synthesis can alternatively be conducted in an intramolecular fashion by taking advantage of a removable tether. In the first examples, sulfonamides, sulfonates [130], and azetidinones [131] were employed as linkers between the two aryl moieties. Recently, phosphinates [132] and siloxanes [133] have been used for this purpose (Scheme 25). 

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