Aryl sulphonates

Aryl sulphonic acids, either free or in the form of tlieir sodium or potassium salts, are converted into the acid chlorides by reaction with phosphorus peutu-chloride or phosphorus oxychloride, for example ... 

Most of the above reactions are used for the cleavage of aryl sulphones. Recently, a note has appeared109 in which the use of potassium metal dispersed ultrasonically in toluene to cleave saturated cyclic sulphones is described. Addition of iodomethane permits the isolation of acyclic alkyl methyl sulphones (as outlined in equation (44)). 

Trost found126 that aryl sulphones containing a range of other functionalities could be successfully desulphonylated without attack at alkenes, esters or nitriles, and without any detectable degree of alkene migration. 

Eisch, Behrooz and Galle196 give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

Details of the conditions used in these reductions are discussed, especially the fact that this is apparently the first example in which the stereochemical aspects of an electrochemical desulphonylation reaction on a complex molecule have been examined. It is likely that further work will be profitable, given suitable substituents on a molecule, since sulphones (especially vinyl and aryl sulphones) should be good candidates for this type of reduction. 

Cycloalkenyl sulphones, reactions of 646 Cycloalkyl aryl sulphones, lithiated 641 Cyclodextrins 59, 72 in asymmetric synthesis of sulphoxides 292... 

Sulphones - see also Acetoxysulphones, /1-Acyloxysulphones, a-Alkoxysulphones, a-Aminosulphones, Azidosulphones, Azosulphones, Azoxysulphones, co-Cyanosulphones, Dialkoxysulphones, a-Diazosulphones, Disulphones, Episulphones, Epoxysulphones, a-Halosulphones, Hydroxysulphones, / -Iminosulphones, Ketosulphones, a-Lithiosulphones, a-Nitrosulphones, /1-Oxosulphones, Poly(olefin suphonejs, Polysulphones, y-Siloxysulphones, Tetrahalosulphones, Trisulphones addition reactions of 642-649, 774-809 alkadienyl - see Alkadienyl sulphones alkenyl - see Alkenyl sulphones alkyl aryl - see Alkyl aryl sulphones alkylthiomethyl - see Alkylthiomethyl sulphones... 

Bis(4-hydroxyphenyl) sulphones butadienyl - see Butadienyl sulphones chiral - see Chiral sulphones complexes of 573 cyclic - see Cyclic sulphones cycloalkenyl - see Cycloalkenyl sulphones cycloalkyl aryl - see Cycloalkyl aryl sulphones... 

A further series of reactions involving strong bases and sulphones is the rearrangement that occurs when aryl sulphones containing an a-methyl group are induced to give substituted arylsulphinic acids This reaction is now known as the Truce rearrangement. 

The ratio ARH/ARj (monoalkylation/dialkylation) should depend principally on the electrophilic capability of RX. Thus it has been shown that in the case of t-butyl halides (due to the chemical and electrochemical stability of t-butyl free radical) the yield of mono alkylation is often good. Naturally, aryl sulphones may also be employed in the role of RX-type compounds. Indeed, the t-butylation of pyrene can be performed when reduced cathodically in the presence of CgHjSOjBu-t. Other alkylation reactions are also possible with sulphones possessing an ArS02 moiety bound to a tertiary carbon. In contrast, coupling reactions via redox catalysis do not occur in a good yield with primary and secondary sulphones. This is probably due to the disappearance of the mediator anion radical due to proton transfer from the acidic sulphone. 

Selected examples of the soliddiquid two-phase synthesis of aryl sulphones... 

However, in an intriguing reaction promoted by the para-nitro groups of the aryl-sulphone (1) (Scheme 6.25), the initial Michael adduct derived from acrylic esters produces the diarylpropanoic esters (2), together with the diesters (3) (from methyl or ethyl acrylate) [39]. A similar addition-rearrangement reaction has been observed with l-aryl-2-(4-nitrobenzenesulphonyl)ethanones [40]. Additionally, reaction of the sulphonylethanone with two equivalents of the acrylic ester produces a 4-hydroxy-1,4-diarylcyclohexane-1,3-dicarboxylate. 

Alkyl aryl sulphones (typical procedure). Method A. A solution of NajTe (prepared by heating a mixture of Te (0.13 g, 1 mmol), Rongalite (0.79 g, 5 mmol) and aqueous 1 M NaOH (15 mL)) is added dropwise to a stirred solution of TsCl (1 mmol) and BzEtjN+CF (0.022 g, 0.1 mmol) in THF (10 mL) at room temperature under Nj. An instantaneous reaction occurs and the colour of the mixture changes to deep black. After stirring for 5 min. 

Electrochemical reduction of aryl sulphones in methanol leads to cleavage of one carbon-sulphur bond in a two-electron process. Alkyl aryl sulphones with an electron donating substituent in the aryl ring give the arenesulphinic acid and an alkane [68, 69]. Methyl phenyl sulphone and alkyl aryl sulphones with an electron withdrawing substituent in the aryl ring are cleaved to the substituted arene and the alkylsulphinic acid [70], see Scheme 5.2. In addition, a bulky orfAo-substituent such as tert.-butyl favours cleavage to the arene and alkanesulphinic acid [71]. 

Retinol Derivatives. Aryl sulphones have been used in two new syntheses in the vitamin A series. Reaction of /8-cyclocitryl phenyl sulphone (102) with the bromo-compound (103) gives the intermediate sulphone (104), which on base-catalysed elimination affords methyl retinoate (98). Alternatively retinol (99) has been prepared in high yield by condensation of the C15 bromide (105) with the C5 hydroxy-sulphone (106), followed by elimination of sulphinic acid. The syntheses... 

Nevertheless, at 130°C (3h), the silica-alumina does not produce appreciable conversion of 1. When the aryl sulphonic derivative of silica is selected as catalyst, quantitative yields are obtained for 3h at 130°C or for lh at 160°C, being in both cases the selectivity of the reaction directed to the hydrolysis product 3. With the sulphonic resin Amberlist 15 the conversion of the oxime 1 depends on the temperature of the reaction thus, at 130"C (3h) the yield is close to 50% being the major product the acetophenone (2), while at 160°C (lh) the yield is 73%, and the two products 2 and 3 are detected. 

Sulphones (—SO ). Aliphatic, vinyl and aryl sulphones have been extensively characterized (Tables A.4.1-A.4.3).6 9 29 40 46-54 Reported chemical shifts cover a range of about 80 ppm (—40 to +40 ppm, with the only known exception of thiirane 1,1-dioxide, (CHa SO whose chemical shift is —88 ppm47). Signals are relatively sharp, with line widths varying from a few hertz to about 1,500 Hz. 

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