Allyl sulphonic acid

Benzylic, allylic and propargylic positions enhance the cathodic cleavage rate of C— heteroatom bonds as, for example, in the reduction of benzylic and allylic halides or alcohols56. Similar activated sulphones, due to their acidity, are in a class apart. Figure 8 shows the similitude between the cathodic behaviour of an allylic sulphone and its isomer, i.e., the corresponding vinylic sulphone when the electrolyses are run in an aprotic solvent. However, in the presence of an excess of proton donor, discrepancies appear. 

One potentially important example of CIDNP in products resulting from a radical pair formed by electron transfer involves a quinone, anthraquinone j5-sulphonic acid (23). When irradiated in the presence of the cis-syn dimer of 1,3-dimethylthymine (24), enhanced absorption due to vinylic protons and emission from the allylic methyls of the monomer (25) produced can be observed (Roth and Lamola, 1972). The phase of the polarizations fits Kaptein s rules for intermediate X... 

Allyl sulphones can be converted to dienes by alkylation and elimination of sulphinic acid under basic conditions (equation 64)105. Several vitamin A related polyenes have been synthesized following this two-step protocol (Table 10)106. The poor leaving-group ability of the arylsulphonyl group requires treatment with strong base for elimination. However, elimination of the allylsulphonyl group takes place readily under palladium catalysis (equation 65)107. Vinyl sulphones can be converted to dienes via Michael addition, alkylation with allyl halides and elimination of sulphinic acid sequence (equation 66)108. 

An alternative deprotection method, which proceeds without prior isomerisation, involves heating under reflux the allyl ether in aqueous methanol with palladium/activated charcoal in the presence of toluene-p-sulphonic acid.79... 

Deprotection of allyl aryl ethers is accomplished by protonolysis with palladium on activated charcoal in methanol solution in the presence of toluene-p-sulphonic acid,42 or by reduction with sodium bis(2-methoxy-ethoxy)aluminium hydride in toluene solution43 (Aldrich). This latter reagent also cleaves aryl benzyl ethers. 

A rapid method for resolving ( + )-carvone through the derivative (151) has been described. Reaction of carvone with allyl Grignard reagents leads to the expected products (152), and these can be aromatized with toluene-p-sulphonic acid to (153) and (154). An improved method for the preparation of carvone 1,3,8-tribromide [(155) see Vol. 1, p. 31] consists in treating the dibromide (156), obtained by Wallach from dihydrocarvone (148), with phenyltrimethylammonium tribromide in tetrahydrofuran. ... 

Dehydration of compounds (653 R = H or Ph) by toluene-p-sulphonic acid in benzene proceeds by homo-allylic rearrangement to give (654 R = H or Ph) some unrearranged olefin is obtained in the dehydration of (653 R = Ph). The cycliza-tion of ethyl (cyclo-oct-4-enylidene) acetate with BFajOEtj in hot benzene affords (655) and the corresponding acid (656). The bridgehead cation (657) is the presumed reaction intermediate. Aluminium chloride-catalysed cyclization of the lactone (658) resulted in the stereospecific formation of the carboxylic acid (660) the epimeric lactone (659) produced a mixture of a hexahydrofluorene carboxylic acid and the epimeric benzobicyclononene acid (661) mechanisms are discussed. 

The tributyl allylstannanes (44), prepared from allylic sulphones with allyl inversion, have been shown to add, again with allyl inversion, to trioxan in the presence of a Lewis acid (Scheme 18). The authors claim this as the first report... 

Certain a-hydroxyalkylthioketals eliminate benzenethiol under treatment with a sulphonic acid to provide a regiospecific approach to a-phenylthioketones (Scheme 31), On the other hand, j8-hydroxyalkyl phenyl sulphides eliminate water, with migration of the PhS group, to yield allyl sulphides. ... 

Cathodic behaviour of allylic and propargylic sulphones in low-acidity... 

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