Homoallylic sulfones

This route to 1,3-dienes is more efficient than the more direct one employing homoallyl sulfones. 

In Scheme 13.17. decarboxylative Claisen rearrangement (dCr) reaction of myrtenyl tosylacetate 19 is shown. The sole product obtained for this tandem transformation was that of delivery of the ketene acetal to the allylic double bond in a sense anti to the more sterically demanding dimethyl-substituted methano bridge. Subsequent decarboxylation in situ gave the homoallylic sulfone 20. This reaction gave similar yields when carried out under microwave conditions. 

Allyl esters (R)-39 undergo stereospecific palladium-catalyzed decarboxylative allylation to give the corresponding homoallylic sulfones (5)-40 (Scheme 22.11). In contrast with reactions that require strongly basic reagents like BuLi and a low temperature (—105°C see Scheme 22.10), the palladium-catalyzed decarboxylation occurs under neutral conditions and at room temperature. ... 

Sulfonic peracids (66) have also been applied recently to the preparation of acid sensitive oxiranes and for the epoxidation of allylic and homoallylic alcohols, as well as relatively unreactive a, p - unsaturated ketones. These reagents, prepared in situ from the corresponding sulfonyl imidazolides 65, promote the same sense of diastereoselectivity as the conventional peracids, but often to a higher degree. In particular, the epoxidation of certain A -3-ketosteroids (e.g., 67) with sulfonic peracids 66 resulted in the formation of oxirane products (e.g., 68) in remarkably high diastereomeric excess. This increased selectivity is most likely the result of the considerable steric requirements about the sulfur atom, which enhances non-bonded interactions believed to be operative in the diastereoselection mechanism <96TET2957>. 

A further improvement on the tetrahydropyranol formation was made by using the Amberlite IR-120 Plus resin—an acidic resin with a sulfonic acid moiety, in which a mixture of an aldehyde and homoallyl alcohol in water, in the presence of the resin and under sonication, yielded the desired tetrahydropyranol derivatives.111... 

In order to further extend the generality of our method, a functionalized allylsilane was also reacted with sulfone It. Under the same optimized conditions, the corresponding homoallylic amine was obtained and subsequently subjected to... 

Scheme 5 Allylation of Alloc-derived sulfones and ring-closing metathesis of an Alloc-protected homoallylic amine...

Desulfonylation homoallylic alcohols.24 Allyl sulfones (2), prepared as shown, undergo desulfonylation by sodium borohydride in the presence of catalytic amounts of Pd(0). This reaction was used to prepare homoallylic alcohols (3) from allylic p-tolyl sulfones (1). 

A similar effect is observed in the osmylation of allylamides bearing a bis-homoallylically located sulfoxide group94. In this case the asymmetric 1,5-induction of the stereogenic sulfur atom totally overwhelms the weak bias of the allylic chirality. The concomitant sulfoxide-to-sulfone transformation suggests sulfoxide involvement in the oxidation mechanism. In this example, as well as in the previous one, replacement of the sulfur-based directing group by a sulfone moiety leads to a drop in diastereoface differentiation. 

Trisubstituted tetrahydrofurans can be synthesized by the intramolecular 5-endo-tr g attack of alkoxides on vinylic sulfones. Starting from 3-benzenesulfonyl homoallylic alcohols, the cycliza-tion is carried out at 25 °C in tetrahydrofuran, using potassium tert-butoxide as the base143 145. 

The nucleophilic addition of lithiated allyl phenyl sulfone to nitrones at 0 °C afforded 4-(phenylsulfonyl)isoxazol-idines as major products. The process probably involves the isomerization of the allylsulfonyl moiety of the initially formed hydroxylamine anion to vinylsulfone which then undergoes intramolecular Michael addition. For example, the chiral nitrone 536 afforded isoxazolidine 537 with high diastereoselectivity (Equation 88) <2005T3335>. When the same reaction was carried out in the presence of hexamethylphosphoramide (HMPA) at —80°C, the anti-a-sulfonyl homoallyl hydroxylamine was obtained. 

Homoallylic amine derivatives are obtained from reaction of a-aminoalkyl / -tolyl sulfones and allylsilanes. ... 

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