Bisalkynyl benzoates

The synthesis of bisalkynyl benzoates from bisalkynyliodonium triflates with sodium benzoate or p-nitrobenzoate in dichloromethane has also been reported (equation 89)43. The bisalkynyl esters are sensitive to hydration of the triple bonds, especially in solution, and have been isolated only in low yields. When R = H, monobenzoate derivatives are also obtained. 

Alkynyl carboxylate esters, 75, are obtained in the reaction of lithium acetylides with bis(acyloxy)iodobenzene, 73 [Eq. (32)] [59], These reactions are likely to proceed through the intermediacy of the respective alkynyliodonium carboxylates (74), although no such salts have been isolated to date as they spontaneously decompose, via loss of iodobenzene, to the alkynyl carboxylates, 75. Only benzoate esters (75 R = CgHj) are sufficiently stable to isolate and store pure for longer periods. Simple alkylcarboxylates such as acetates are not stable although the hindered pivaloate ester (65 R = t-Bu, R = t-Bu) has been isolated in low yield [59]. Among the reasons for the instability of these esters is their sensitivity to moisture they both readily add water and undergo subsequent hydrolyses [60]. Because of the sensitivity to moisture, the isolated yield [41] of bisalkynyl benzoates, 76, from the bisalkynyliodonium triflates, 35, is only 6-15% [Eq. (33)]. 

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See also in sourсe #XX -- [ ]

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