Sulfenates, propargylic

Following studies on the rearrangement of allylic arenesulfinates, Braverman and coworkers have investigated a number of natural extensions of this unique transformation, including the predictable [2,3] sigma tropic rearrangements of allylic sulfenates to sulfoxides and of propargylic sulfenates and sulfinates to allenic sulfoxides and sulfones respectively. The last reaction is described below, while the other two are described in Chapter 14. 

C. [2,3]-Sigmatropic Rearrangements of Propargylic Sulfenates to Allenic Sulfoxides... 

The synthetic utility of the remarkably facile and efficient [2,3]-sigmatropic rearrangement of propargylic sulfenates has been further demonstrated in a variety of preparations and interesting reactions of allenyl sulfoxides , including the preparation of vinylallenes " which are useful intermediates in organic synthesis in general and natural polyenes, such as Vitamins A and D, in particular Two typical examples, taken... 

Two different types of substrates are used here, propargyl sulfenates and propargyl sulfmates. In both cases often the propargylic esters are prepared and then converted to the allenes in situ. 

An example involving propargyl sulfenates is the reaction of 143 leading to the vinylallene 144 [379] (Scheme 1.64) related conversions have been reported [380] and often the propargyl sulfenates are prepared in situ and isomerize at low temperatures [381-424]. 

A number of different methods have been used to synthesize racemic sulfinyl dienes. They involve oxidation of dienylthioethers [119], reactions of a-sulfinyl carbanions with different electrophiles [60, 120], sulfoxide-sulfenate rearrangements of propargylic sulfenates followed by isomerization of the resulting sulfinylallenes [121], and reactions of sulfolenes with Grignard reagents [122]. 

Synthetic Utility of the Propargylic Sulfenate-to-Allene Sulfoxide Rearrangement... 

Scheme 13 [2,3]Sigmatropic rearrangements of nitroaryl propargyl sulfenates to allene sulfoxides and their cycloaddition reactions...

Scheme 15 One-pot stereocontrolled synthesis of 9-cis-retinoids via [2,3]sigmatropic rearrangement of propargylic sulfenates...

The [2,3]sigmatropic rearrangement of propargylic sulfenates can be applied for the preparation of a variety of functionaUzed allenes, not readily acceptable by other routs. Thus, a number of suMnyl allenecarboxy-lates (67, 68), as new 1,1-diacceptor-substituted allenes, were prepared via a [2,3]sigmatropic rearrangement of the corresponding sulfenate esters (65, 66) (Scheme 16) [49,50]. 

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