Dihalides alkyne synthesis from

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Alkyne carbon atoms are sp-hybridized, and the triple bond consists of one sp-sp a bond and two p-p tt bonds. There are relatively few general methods of alkyne synthesis. Two good ones are the alkylation of an acetylide anion with a primary-alkyl halide and the twofold elimination of HX from a vicinal dihalide. 

It was found that the system tcrt-BuOH/0.1 mol% 18C6/petroleum ether is also very useful in alkyne synthesis, starting from 1,2-dihalides (from alkenes) or 1,1-dihalides (from aldehydes or ketones). Advantages are high yields and fairly mild reaction conditions [232,233]. 

Therefore, the last step of our synthesis must be formation of the alkyne from a vicinal dihalide ... 

Don t be confused by this retrosynthetic arrow. It indicates a hypothetical synthetic pathway thinking backward from the product (alkyne). In other words, the previous figure should be read as In the last step of our synthesis, the alkyne can be made from a vicinal dibromide. Now let s try to go backward one more step. We have learned only one way to make a vicinal dihalide, starting with an alkene ... 

The synthesis of an alkyne from either a geminal dihalide or a vicinal dihalide requires a strong base to eliminate two moles of hydrogen hahde. Two suitable reagents for this reaction are sodium amide in hquid ammonia as the solvent and potassium tert-butoxide in dimethyl sulfoxide. 

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