Ethynylation under phase-transfer conditions

Bromination of 1-alkynes with N-bromosuccinimide in the presence of catalytic amounts of silver nitrate, was used first for the bromination of 17-ethynyl steroids.7 Similarly, N-iodosuccinimide led to 17-iodoethynyl steroids, lodination of propiolates in this way has not been studied. A recent method of preparation of 1-iodoalk-l-ynes under phase-transfer conditions involves molecular iodine and copper(l) iodide as catalyst, in the presence of potassium or sodium carbonate as a base. Ethyl 3-iodopropiolate was prepared by this route in 80% yield.8... 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

Dichloroprop-l-yne does not generate chloro(ethynyl)carbene, but instead gives (chlorovinylidene)carbene, under the conditions of phase-transfer catalysis. The (chlorovinylid-ene)carbene undergoes addition to alkenes with the formation of (chlorovinylidene)cyclo-propanes. ... 

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