Acetylene reactions with sodamide

The amide ions are powerful bases and may be used (i) to dehydrohalogenate halo-compounds to alkenes and alkynes, and (ii) to generate reactive anions from terminal acetylenes, and compounds having reactive a-hydrogens (e.g. carbonyl compounds, nitriles, 2-alkylpyridines, etc.) these anions may then be used in a variety of synthetic procedures, e.g. alkylations, reactions with carbonyl components, etc. A further use of the metal amides in liquid ammonia is the formation of other important bases such as sodium triphenylmethide (from sodamide and triphenylmethane). 

Procedures for the preparation of sodamide in liquid ammonia and for its reaction with acetylene to form sodium acetyiide are applicable also to the preparation of... 

Alkynes of chain length longer than two carbons can be formed from acetylene by using sodamide (NaNH2). Sodamide reacts with acetylene in an acid-base type of reaction. The hydrogen attached to the triply-bonded carbon shows appreciable acidity. Hence,... 

Synthesis of Natural Polyacetylenes.—Bohlmann and Weber have reported the synthesis of racemic samples of four polyacetylenic enol-ethers (43), (44), (45), and (46), isolated earlier from Anaphalis species (Scheme 2). The acetonide from the 3-hydroxydihydropyrone (40) was first converted into chloride (41) which with sodamide produced the acetylenic alcohol (42). Successive reaction (Cadiot-Chodkiewicz coupling) of bromohepta-1,3,5-triyne with (42) and treatment with base gave the cis- and /m jr-(43) enol-ethers, which reacted with thionyl chloride to produce cw-(44) and trans- A5)y respectively. Epoxidation of (45) then gave (46). In the same publication. 

For a long time" , it has been known that there is rearrangement of 1-alkynes to 2-alkynes under basic conditions (for instance by alcoholic potassium hydroxide or powdered potassium hydroxide) at 175 C. It has been shown that in fact an equilibrium mixture is obtained . It contains isomeric compounds, mainly the starting 1-alkyne and isomeric 1,2-alkadiene and 2-aIkyne, but the latter, more stable from thermodynamic considerations, is predominant. Therefore the method could be used to prepare 2-alkynes from corresponding 1-alkynes. The reverse reaction is possible disubstituted acetylenes can be converted to sodium derivatives of 1-alkynes by sodium or sodamide . 1-Alkynes are recovered by hydrolysis. We have tried to apply both reactions to prepare acetylenes deuterated in defined positions with high isotopic purity. 

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