Sigmatropic rearrangements 3.3 , propargyl derivatives

Although acyloxy, phosphatyloxy, and tosyl allenones were obtained from the corresponding propargyl alcohol derivatives via silver catalysis through an overall process that resembled [3,3]-sigmatropic rearrangement (see Sections 3.41 and 3.43), the mechanism was not fully proved and is still in question. 

The [2,3]sigmatropic rearrangement of sulfonium ylide (24) derived from rhodium-catalyzed decomposition of ethyl 3,3,3-trifluoro-2-diazopropanoate (23) in the presence of propargyl sulfide (22a) affords the corresponding functionalized CF3-containing carboxylic ester sulfide (25a). The latter was... 

A-Propargyl dithiocarbonates (xanthates) 533 bearing a variety of substituents were convenient precursors of 1,3-dithiole-2-ylidene derivatives 534 by reaction with active methylene compounds involving a [3,3]-sigmatropic rearrangement (Equation 64) <1995TL5171>. In all cases except dibenzoylmethane, a mixture of regioisomers was obtained, with double bond exo or endo. 

An interesting development in the lithiated cyanohydrin ether approach to acyl carbanion equivalents involves the [2,3] sigmatropic rearrangement of the anions derived from allyl- or propargyl-cyanohydrin ethers/ Scheme 2 shows an example of the application of this process in the synthesis of y-dicarbonyl compounds or their monoenol ethers. ... 

Compound 79 was obtained from the corresponding propargylic derivative (1 equiv) by treatment with diphenylphosphine chloride (1 equiv) in dichloromethane solution at -78 °C for 1 h, in the presence of triethylamine (1 equiv). After [2,3]-sigmatropic rearrangement, the reaction mixture was heated at 37 °C in the presence of cyclohexadiene (0.01 M) for 16 h, tm = 8 h) to give the corresponding phosphine oxide toluene derivative 80 in 60% yield. 

In another related and well-known [3,3]-sigmatropic shift usually performed under thermal conditions, the propargyl-Claisen rearrangement,62 silver salts were also able to catalyze the reaction. Silver tetrafluoroborate and hexafluoroantimonate proved to be the best catalysts for this reaction, leading quantitatively to allenic p-ketoesters when starting from propargyl ethers derived from p-ketoesters (Scheme 3.41).63 64... 

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