Sulfonates, aryl arene

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

In the coupling of more challenging substrates, reduction of the aryl halide is frequently observed [21]. Specifically, in the reaction of electron-rich aryl halides or sulfonates, reduced arene is a major by-product. Presumably, this side-product arises when the palladium amide can undergo /1-hydride elimination to generate an imine and a palladium (II) aryl hydride (Scheme 2). Subse-... 

Diaryl sulfones. Aryl sulfonyl bromides (but not sulfonyl chlorides) react with silver trifluoromethanesulfonate in nitromethane at 0° to form unstable mixed sulfonic anhydrides (c/ 4, 533-534). These react with arenes (threefold excess) at the same temperature to give diaryl sulfones usually in yields of 80-100%. 

Simply mixing solutions of the tetracationic diphosphine (175) with a tetraanionic calix[4]arene leads to the formation of supramolecular heterocapsules that can bind a transition metal ion within the cavity of the assembly, providing a new class of potential supramolecular catalysts. Sulfonated aryl-phosphines and -diphosphines form supramolecular adducts with cyclodextrins that are also of interest as new ligand systems,and the mechanism of such inclusion processes has attracted a theoretical study. ... 

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). 

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). 

The facility of arene reductive elimination underpins numerous C-C, C-O and C-N bond-forming reactions, which may be catalysed by late transition metals, in particular palladium (Figure 4.10). Although there are many variants, the general reaction scheme involves introduction of the aryl in electrophilic form via oxidative addition of an aryl halide (or sulfonate), substitution of the palladium halide by a nucleophile (which may also be carbon based) followed by reductive elimination. It is noteworthy that nucleophilic aromatic substitution in the absence of such catalysts can be difficult. 

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

Other related reactions are the substitutions of aliphatic sulfonate esters by arenes and the epoxide-opening with benzenes catalyzed by gold. In both cases, the aryl groups are the nucleophiles that attack the gold-coordinated sulfonate esters or epoxides, respectively. 

Much of the research on the SbCls-catalyzed halogenation of arenes has focused on the chlorination and bromination of perfluoroalkyl-substituted aromatics [14]. The reaction of organic disulfides with electron-rich aromatic compounds under catalysis with SbCls and AgSbFg affords unsymmetrical aryl sulfides in modest yields [15a]. Electrophilic sulfinylation and sulfonation can be similarly effected by SbCls [15a-c]. Alkyl- and halobenzenes give thiocyano derivatives when treated with a mixture of SbCls and Pb(SCN)2 in CCI4 [16],... 

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]. 

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