91Ó°ÊÓ

Acetylene groups can be made reactive by deprotonation using a strong base. The acetylide anion hence formed, can act as a nucleophile and undergo several nucleophilic substitution reactions.The general reaction of acetylide ions with alkyl halide and epoxide is shown below:

Reaction of acetylide anion with alkyl halide and epoxide

a.

Cyclohexene can undergo epoxidation upon treatment with mCPBA. It can be further treated with an acetylide anion and oxidized with PCC to achieve the desired compound. The reaction is shown below:

Synthetic pathway of reaction a.

b.

The given starting material is treated with sodium hydride to form the acetylide anion, and the reaction proceeds further as shown below:

Synthetic pathway of reaction b

c.

The syn-addition of hydrogen to an alkyne can be done with the Lindlar catalyst. The desired compound is obtained upon the series of reactions, starting with acetylene, as given below:

Synthetic pathway of reaction c.

d.

The reaction proceeds in the same manner as the previous reaction till the second last step. Since the desired alkene is in its transconformation, the reagent that is used for the anti-addition of hydrogen is sodium in liquid ammonia. The trans alkene is further oxidized with PCC to obtain the desired product. The sequence of the reaction is given below:

Synthetic pathway of reaction d.