Substituted Sulfones

Sulfonation. Aniline reacts with sulfuric acid at high temperatures to form -aminoben2enesulfonic acid (sulfanilic acid [121 -57-3]). The initial product, aniline sulfate, rearranges to the ring-substituted sulfonic acid (40). If the para position is blocked, the (9-aminoben2enesulfonic acid derivative is isolated. Aminosulfonic acids of high purity have been prepared by sulfonating a mixture of the aromatic amine and sulfolane with sulfuric acid at 180-190°C (41). 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

Acid catalysed rearrangement of the tetrahydro 1-benzazepine sulfonamides 52 gave the 9-substituted sulfone derivatives 53 plus, in the case of 52b, the 7-substituted isomeric derivative... 

Several new types of Ge-C cleavage reactions have been reported where the departing organic group is a functionalized species. Secondary amines undergo nucleophilic addition to germanium-substituted sulfones to yield sulfolanes... 

LA Carpino, J Xia, C Zhang, A El-Faham. Organophosphorus and nitro-substituted sulfonate esters of l-hydroxy-7-azabenzotriazole as highly efficient fast-acting peptide coupling reagents. J Org Chem 69, 62, 2004. 

Replacement of tppts by the fluoro substituted sulfonated ligand 4 [Table 2 94% (n=l) and 6% (n=0)] in the rhodium-catalysed hydroformylation of 1-hexene in a two phase system increased the selectivity to linear aldehyde n-heptanal from 86% to 93% at the low P/Rh molar ratio of 7.5/1.75,76 The Rh/4 catalyst was quantitatively recovered after the reaction by simple decantation.75,76 The moderate increase of the n/i ratio is of interest when one considers that ligand 4 is mainly present as the disulfonated species (94%) compared to the trisulfonated compound tppts and that tris(4-fluorophenyl)phosphine is less basic (pKa=1.97) than triphenylphosphine (pKa=2.73).376 In rhodium-catalysed hydroformylation reactions in organic solvents it is known that electron withdrawing substituents, which increase the -acidity of the ligand, give rise to an increase in the n/i ratio.377 379... 

Another type of reactivity is due to the enhanced nucleophilicity of the hydroxyl group of o-iodosobenzoic acid. For example, o-iodosobenzoic acid reacts with silyl triflate or other silyl sulfonates to afford O-substituted sulfonates [56]. 

One synthesis of benzofurans is based on cyclofragmentation. An appropriately substituted sulfone is used as a nucleophile in intramolecular ring opening of an epoxide. The resulting molecule loses a sulfinate and formaldehyde. By immobilization of the sulfinate on a resin this sequence can be used for the cleavage of benzofurans from solid supports [112] (Scheme 6.1.31). 

Unlike most other electrophilic aromatic substitutions, sulfonation is often reversible (see Section 17-4). When one sample of toluene is sulfonated at 0 °C and another sample is sulfonated at 100 °C, the following ratios of substitution products result ... 

Independently, Pal and coworkers [109] have shown that this approach can be performed in water as a solvent and that it is also fairly general for the synthesis of 2-substituted sulfonated indoles 139 (Scheme 52). 

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