Propargyl ketones, rearrangements with

A little-explored route to allenylsilanes utilizes tosylhydrazone derivatives of tri-methylsilyl alkynyl ketones [52]. Treatment with NaBH3CN in acidic medium leads to transient propargylic diazines, which rearrange with loss of nitrogen (Eq. 9.44). 

When simple aldehydes were converted to allylic alcohols, they could be transformed to the corresponding trichloroacetimidates and subjected to thermal rearrangement to provide aUyl amines. The aUyl amine functionality was also accessible from enantio-selective reduction of propargyl ketones followed by conversion to the phthalamide derivative and reduction of the triple bond. Ozonolysis of these substrates provided the corresponding a-amino methyl esters in good yield (eq 48). As with the allyl alcohols, optically active substrates were treated with ozone without loss of enantiopurity of the chiral center. 

The reaction of aldehydes or ketones proceed through the six-center electronic transfer with propargylic-allenic rearrangement [3]. 

When X=OH, this conversion of acetylenic alcohols to unsaturated aldehydes or ketones is called the Meyer-Schuster rearrangement The propargyl rearrangement can also go the other way that is, 1-haloalkenes, treated with organocopper compounds, give alkynes. ... 

The acidity of the propargylic proton of the starting compound 18 allows the equilibration with the allene 19 induced by bases such as tertiary amines or alcoholates (Scheme 7.4). Such prototropic rearrangements furnish the title compounds 19 with at least one proton at the terminal carbon atom, often in good yields. The EWG group involves carboxylic acids [33], esters [34], ketones [35, 36], isonitriles [37], sul-fones [38], sulfoxides [39, 40] and phosphonates [41], The oxidation of easily accessi-... 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

The thiophilic addition of Grignard reagents was also carried out with S-allylic and propargylic dithioates. In these cases a [2, 3] sigmatropic rearrangement of the magnesiocarbanion occurred, and alkylation at sulfur yielded the dithioacetals of (i-unsaturated ketones [334] or of allenic ketones [335]. 

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