Unsaturated Sulphones

Michael addition reactions of allyl sulphones and a/3-unsaturated carbonyl compounds provide useful starting points in synthesis, illustrated in a synthesis of chrysanthemate ester [Me2C=CHCH2S02ph -I- Me2C=CHC02R - MeaC= CHCH(S02Ph)CMe2CH2C02R cis- and tm/is-cyclopropane esters].  

Tamaru, M. Kagotani, and Z. Yoshida,/. Chem. Soc., Chem. Commun., 1978,367. 

Addition reactions of vinyl sulphones (Diels-Alder addition, [2 -i- 2]-photocycloaddition, and conventional functionalization processes, e.g. IN 3 2-azido-l-iodoalkyl sulphones °°) and substitution reactions of / -halogeno-vinyl sulphones have been reported. A point of interest in the cycloaddition study is the effect of ( )-(Z) equilibration in hindering the participation of simple vinyl sulphones in photocycloaddition reactions. Elimination of SO2 has been observed in the photolysis of 3-oxo-alk-l-enyl sulphones in benzene, giving radicals which attack the solvent.  

Ladurec, P. Rioult, and J. VUdle, Bull. Soc. chim. France, 1973, 637. 

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As mentioned in Section B, under polarography, a, /J-unsaturated sulphones undergo reduction of the double bond. 

A much improved synthesis of perfluoroalkanesulphonyl fluorides from sulphones has been published. This involves the electrolysis of cyclic unsaturated sulphones in anhydrous HF at 8-10°C using a potential of 5-7 volts. Thus, butadiene sulphone was oxidized to perfluorobutanesulphonyl fluoride in quantitative yield211 (equation 94). 

The structural requirements of sulphones to react cathodically and to possess specific electrochemical properties are summarized in Scheme 1. In other words, condition (a) means that aromatic sulphones and a unsaturated sulphones are electroactive, i.e., electron transfer to the LUMO leads to the anion radical, but a cleavage reaction (see b) is mainly observed when R S02 " is a fairly good leaving group. Consequently, the two main classes of electroactive sulphones may react differently with aromatic sulphones, ArS02—R, cleavage is strongly favoured, while with unsaturated sulphones ... 

Unsaturated sulphone Reduction potential (Electrolyte) Product Coulometry (F mol-1) Ref. 

Aromatic unsaturated sulphones Reduction potentials (electrolyte)4 Main product Coulometry (FmoL1) Ref. 

More data are obviously necessary to elucidate carefully the cathodic behaviour of the model molecule 23. The complexity of the many chemical pathways shown in Scheme 2 may illustrate the electrochemical reactivity of unsaturated sulphones in general. 

Some polarographic work has been performed on sulphones in which, evidently, other functional groups suffered reduction. Thus the vinyl group rather than the sulphone group of methyl vinyl sulphone was reduced polarographically -. The unsaturated group of a, -unsaturated sulphones was also reduced . Halogen substituents have been... 

The sulphone (10 mmol) and TEBA-C1 (0.45 g, 2 mmol) in CH2CI2 (20 ml) are stirred with aqueous NaOH (50%, 20 ml) for 15 min at room temperature. The aryl aldehyde (30 mmol) in CH2C12 (5 ml) is then added dropwise and the mixture is stirred for a further 2-6 h at room temperature. On completion of the reaction, the mixture is poured into H20 (50 ml) and extracted with Et20 (3 x 50 ml). The organic solutions are washed well with HzO, dried (Na2S04), and evaporated to yield the a,p-unsaturated sulphone (e.g. from PhS02Me and PhCHO, 86% 2-naphthylCHO, 85%). 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

Some functional groups that are sensitive to reaction with strong bases, like alkoxides, undergo reaction under these reaction conditions380,381. Thus 2-chloroethanesulphonyl chloride reacts with alkoxides to give the unsaturated sulphonate ester, as indicated in equation 84. Such side-reactions may be averted by reaction of the sulphonyl chloride, or fluoride, with the trimethylsilyl derivative of the alcohol382, as indicated by equation 85. The derivative may be formed under mild conditions from the alcohol. 

The base-catalysed isomerization of /3-epoxy-sulphones (126) to y-hydroxy-ajS-unsaturated sulphones (127) was shown by kinetic data, an isotope effect, and stereochemistry to involve an intramolecular suprafacial 1 -> 3 hydrogen migration, with a carbanion-like transition state. " 4-Hydroxy-2-sulpholen, 3-hydroxy-4-chlorosulpholan, and 3,4-epoxysulpholan were found to react with thiolates to give mixtures of cis- and tran5-3-hydroxy-4-(alkylthio)sulpholans in a ratio of 2 3." ... 

The easy isomerization of the sulphone-stabilizing anion generated from the phenyl sulphone (62) has been put to good use in a novel route to alk-2-enes (65) in reasonable yields (Scheme 15). The anion is alkylated stereo- and regio-specifically to give the a(S-unsaturated sulphone (63) on isomerization of the intermediate (64) with catalytic amounts of potassium t-butoxide. Small amounts of the a,a-dialkylated products are also formed. Reductive removal of the phenyl-sulphone moiety by lithium-ethylamine in the usual way, or better under milder conditions with potassium-graphite, gives the product. 

A remarkably stereospecific elimination has been utilized in the synthesis of ( )-presqualene alcohol and ( )-prephytoene alcohol. The process is based on the addition of the anion derived from a Py-unsaturated phenylsulphone to an aP-unsaturated ester. The intermediate anion (24) cyclizes to give the truns-cyclopropane-carboxylic ester (25), the geometry about the double bond of the unsaturated sulphone... 

When we used a,P-unsaturated sulphones and phosphonates as well as aldehydes (acyloin reaction) as electrophiles to trap the metalated aminonitriles, moderate to good ee-values were obtained and we are still engaged to optimize these variants [58]. 

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