Sulfones, vinyl reaction with Grignard reagents

TABLE 3. Cross-coupling reaction of vinyl sulfones with Grignard reagents ... 

The procedure iliustrated here is representative of a generai and versatile method for the preparation of 2-substituted tetrahydrofurans and tetrahydropyrans from cyclic ether sulfones and the appropriate alkynyl, vinyl, or aryl Grignard reagent. From the examples shown in the Table and others previously reported, - a selectivity for the trans-product is observed with 6-substituted tetrahydropyrans irrespective of the initial geometry of the sulfone. This implies the presence of a common reaction intermediate such as an oxonium ion which is trapped by preferred axial bond... 

Vinylic sulfones undergo the same reaction especially when allylic, benzylic or t-alkylithium reagents are employed. One case of a vinyl sulfone deserves special mention - . When phenyl trans-3-bromopropenyl sulfone is treated with certain Grignard reagents it undergoes an alkylating cyclization ... 

Lithiation of vinylic sulfones. Phenyl vinyl sulfones (1), prepared as indicated, react with methyllithium regiospecifically at — 95° at the a-vinyl position to give the lithium derivatives 2. As expected, 2 can be alkylated to give 3. The reaction of 2 with enolizable carbonyl compounds proceeds more satisfactorily by prior conversion to the vinylic Grignard reagent a. This sequence constitutes a route to disubstituted alkenes, since a sulfone group is reductively cleaved by sodium amalgam (7, 326). ... 

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