Other Phase Transfer Reactions of Sulfur Containing Substances

5-Diphenyl-l,4-thiodioxane-l-oxide [21] and the corresponding sulfone (1,1-dioxide) [22] have been isolated in 12% and 48% yields respectively from phase transfer reactions containing sodium hydroxide, benzaldehyde, and either dimethyl sulfoxide or dimethyl sulfone. Apparently, an a,j3-unsaturated sulfone is produced in the first condensation step and the jS-hydroxysulfone which results from a second condensation step undergoes an intramolecular Michael addition as shown in equation 13.12. 

8 Other Phase Transfer Reactions of Sulfur Containing Substances 

Alkyl p-tolyl sulfones have been prepared by nucleophilic addition of the p-tolyl sul-finate anion to primary, allylic, and benzylic halides in tetrahydrofuran [23]. Although these reactions were conducted in the presence of a stoichiometric amount of quaternary ammonium salt, it seems clear that the reaction could be catalytic and is therefore included here. The reaction is formulated in equation 13.13 and several examples of the condensation are shown in Table 13.9. 

Unsymmetrical a-haloalkyl p-tolyl sulfones have likewise been prepared under phase transfer conditions (see Eq. 13.14) [24]. Thus, a-halomethyl p-tolyl sulfones are deprotonated to form a carbanion which reacts with an alkyl halide to give product. a-Halo-a-sulfonylcarbanions apparently are not prone to undergo facile a-elimina- 

A ring closure similar to that yielding a,]3-epoxysulfones (Eq. 13.16) is expected in the phase transfer reaction of phenyl vinyl sulfone with a-chloropropionitrile. Under basic conditions, the nitrile is deprotonated and then adds in the Michael sense to the a,j3-unsaturated sulfone. Protonation of the intermediate a-sulfonylcarbanion yields the simple Michael adduct, (Eq. 13.17), whereas intramolecular nucleophilic substitution would lead to sulfonylcyclopropanes (Eq. 13.18). The former process is favored over the latter to such an extent that less than a 10% yield of cyclopropanes are isolated in this reaction [27]. 

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Other Phase Transfer Reactions of Sulfur Containing Substances Table 13.8. Synthesis of sulfones by condensation reaction [20] ... 

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