Allenes propargylic rearrangement

Phosphaallenes can be synthesized in the same way as 1,3-diaryl-substituted allenes following an aluminium-catalyzed propargyl rearrangement. Using sodium hydroxide-activated aluminium oxide (125), the synthesis is suitable on an enlarged scale without any detectable by-products [Eq. (63)]. A similar proton migration within a coordinated phosphaalkyne was reported recently (126). 

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

The synthetically most useful oxygen-sulfur transpositions (equation 16) are the allyl sulfenate-allyl sulfoxide and the propargyl sulfenate-allene sulfoxide rearrangements, the driving force of both being the formation of the strong S=0 bond at the cost of the weak O—S bond (Scheme 12). ... 

In the following steps (eq 7), we observed two HCl-catalyzed processes an acetylenic-allene rearrangement (to 10) and an allenic-acetylene rearrangement (to 11). While both 10 and 11 were easily identified by their characteristic NMR signals and could be distilled as a mixture without decomposition, only the final acetylene derivative (11) could be isolated in pure form after fractional distillation. Propargyl bromide reacted similarly with the three-coordinate phosphine, but in this case all of the chemical transformations occurred very rapidly and only the final acetylene phosphoranimine (11) could be isolated. 

Similarly alkylation (55) of l-N-pyrrolidino-2-methyl-l-propene (22) with propargyl bromide gave initial N alkylation to (23) with subsequent rearrangement to the allene (24). 

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... 

Analogous with the rearrangement of allylic sulfoxides is the [2,3]-sigmatropic rearrangement of propargylic sulfoxides to allenic sulfenates. This process, which has been relatively little studied so far, appears to be the first step in the facile and quantitative rearrangement of sulfoxide 98 to the hemithioacetal 101 (equation 45)167. This reaction,... 

Rearrangement of acetylenic sulphenates to the allenic sulphoxides 151 was discovered when the synthesis of propargylic ester of trichloromethanesulphenic acid 152 was attempted (equation 86). This reaction is of general scope and gives very good yields of allenic sulphoxides (Table 14) from structurally diverse cohols and various sulphenyl chlorides Reaction of alkynols 153 with benzenesulphenyl chloride in the presence... 

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