Base-induced Prototropic Rearrangements

The availability of 3(2)-6(2) from a Glaser-type coupling of 1,5-hexadiyne (1(2)) was used by Sondheimer and Wolovsky [26] to generate the fully conjugated cyclic 

A benzene solution of the cyclic dimer 61 when refluxed with a saturated solution of t-BuOK in BuOH gave a red solution of the bisdehydro[20]annulene 63 [62]. The cyclic trimer 62 was rearranged similarly to tridehydro[30]annulene 64. Both species show characteristic UV-vis spectra [62]. The bisdehydro[20]annulene was partially hydrogenated in benzene solution over a Lindlar catalyst (quinoline-poisoned palladium calcium carbonate catalyst). This procedure led to the [20]an-nulene 65. Similarly, the reduction of tridehydro[30]annulene 64 with Lindlar catalyst yielded the [30]annulene 66 [62]. 

Chart 7.4. [3]Catenate 51, Cavitands 52 and 53 with butadiyne units. 

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Combining the oxidative coupling reaction of a,w-diethynyl compounds to give cyclic poly-ynes with the base-induced prototropic rearrangement of the cyclic... 

Scheme 5.16 Synthesis of vinyl azides by base-induced prototropic rearrangement ...

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-... 

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