Sigmatropic Rearrangement of Propargyl Compounds

The isomerization reactions of alkynes via [2,3]- or [3,3]-sigmatropic rearrangements are probably among the most important methods available for the introduction of the allene group into an organic molecule. The usefulness of this synthetic method [61, 62] and the access to new functionalized allenes [63] have been reviewed recently. 

We found that 43 (R1 = R2 = Me) and 44 lead to a mixture of the diallenes meso-and rac-45, which can be characterized by spectroscopy without doubt at low temperature [104], The isolation of 45 (R1 = R2 = Me) failed because this compound rearranged rapidly at room temperature most probably to the dienyne 46. Braverman et al. [105] analyzed spectroscopically the diallenes 48 resulting from diols 47 and the reagent 44. In one case, even isolation was possible. However, the cumulenes 48 cydize irreversibly to mixtures of the stereoisomers of the stable compounds 49 at room temperature, mostly at lower temperature. 

Because of the usually high temperatures required to rearrange propargyl sulfi-nates to allenyl sulfones, a report about such palladium-catalyzed transformations seems to be promising [106], Even at low temperatures the synthesis and isomerization of trifluoromethanesulfinate 51 are possible if, during the reaction of the ter- 

The reaction of the propargyl alcohols 53 with the reagent 54 furnished the S-alle-nylsulfinylamines 55 in good to excellent yields [108, 109]. Furthermore, the propargyl alcohols can be transformed with sulfur dichloride to the S-allenylsulfmates 56, which isomerize on heating in solution to the diallenyl sulfones 57 [79, 110, 111]. 

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