4-Tolyl sulphones, synthesis

Selected examples of the liquid-phase synthesis of 4-tolyl sulphones... 

Using a soliddiquid two-phase system of the sodium arenesulphinite in 1,2-dimethoxyethane, or in the complete absence of a solvent, permits the use of less reactive haloalkanes [3,4], This is a particularly good method for the preparation of sulphones where the sulphinic acid salts are readily available and, in addition to the synthesis of the tolyl sulphones listed in Table 4.28, it has been used to prepare phenyl sulphones [3]. Phenyl sulphones have also been prepared in good yield using a polymer supported catalyst [5] (Table 4.29). As the system is not poisoned by iodide ions, reactive iodoalkanes can be used and there is the additional advantages in the ease of isolation of the product and the re-use of the catalyst. 

Other examples of reactions of [2 + 2] additions of electron-rich and electron-deficient olefins have been reported which are mechanistically similar to those described above. The reaction of p-toiyl vinyl sulphone with enamines gives trans-aminocyclobutyl p-tolyl sulphone (50). The cyclobutyl sulphones (50) are readily cleaved under hydrolytic conditions, presumably via zwitterionic intermediates to the acyclic (51). The reaction is a useful synthesis of a,a-dialkyl-y-sulphone aldehydes. Alkene phosphonates also function as the electron-deficient partner in reactions with enamines. Diethoxyphosphinylethylene reacts with the enamines to give the [2 + 2] adduct (52). The aminocyclobutylphosphonate (52) is stable, but the amine may be eliminated under rather vigorous basic conditions to give the cyclobutenyl-phosphonate (53). 

Sulphones Used in Syndiesis.— The range of examples of reactions of sulphones discussed in the preceding section makes clear the scope for applications in synthesis. Most applications are based on sulphonyl carbanions, and are covered in the next Chapter, but ring syntheses are illustrated by a novel synthesis of naphthalene that involves the condensation of o-formylbenzyl p-tolyl sulphones... 

Rearranged products of type R2YC = CR1R2 are obtained from the vinyl triazene 112 when R2 is an aiyl group and Rx is hydrogen or methyl and also when R2 is tolyl and Rx is phenyl. The acid-catalysed decomposition of vinyl triazene which occurs in very mild conditions has been exploited as a useful method for the synthesis of vinyl sulphonates (Jones and Maness, 1969, 1970 Modena and Tonellato 1971). 

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