Solvents terminal acetylene synthesis

It is sometimes necessary to protect active sites of acetylenic compounds to achieve the desired reactions. Acetylenic compounds that have an active hydrogen tend to react with heavy-metal salts to form explosive metal acetylides. However, when treated with potassium mercuric tetraiodide or mercuric acetate in organic amines, monosubstituted terminal ethynyl compounds give stable crystalline mercuric salts. These mercuric salts can be purified by recrystallization in organic solvents and used for identification. They can be further converted to lithium acetylides, which are useful tools for chemical synthesis [Eq. (62) 156]. 

Broiiioform as solvent 18, 533 Bromopropioiic acid, synthesis of poly acetylenes, terminal, with — 20, 611... 

Zanina et al. have reported a method for the synthesis of a, acetylenic ketones from terminal alkynes and acid chlorides using cuprous iodide as a catalyst. The use of high temperature and toluene as the solvent in this protocol prompted Kundu and co-workers to develop a new procedure with triethylamine as the solvent and the base, which obviated many of the difficulties and enabled the reactions to be carried out at room temperature (eq 30). Zhang and co-workers have modified the conditions in order to couple monooxalyl chloride with terminal alkynes THE was used as the solvent with 2 equiv of triethylamine and 5 mol % of Cul. It is noteworthy that CuCl, CuBr, and Cul showed similar reactivity, while CuOTf was totally inert. 

The common work-around for this reactivity problem is to use TMS acetylene (25). This reagent is easily handled and the silyl group is readily removed upon treatment with mild base (26 —> 24 R = OMe). Productive monocoupling of 22 and acetylene (21) to afford the terminal alkynes (24) has been achieved by judicious choice of DMF as a reaction solvent. The proposal is that acetylene has high solubility in DMF, and that the high molarity of acetylene compared to starting halide statistically drives the reaction equilibrium toward formation of the desired monocoupled alkyne 24. Use of TMS acetylene is a general solution to the synthesis of monosubstituted alkynes, while the reactions with acetylene itself afforded... 

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