Question

How would you carry out the following transformation? More than one

step is needed.

Short answer

Alkynes are treated with NaNH₂ , ammonia and alkyl halide to form a higher alkyne. This further reacts with hydrogen and Lindlar’s catalyst to form a cis alkene. This alkene is reacted with CH₂I₂and Zn(Cu) to form a cis-disubstituted cyclopropane ring.

Step-by-step solution

Conversion of alkyne to cyclopropane ring

Alkynes are treated with NaNH₂ , ammonia and alkyl halide to form a higher alkyne. This further reacts with hydrogen and Lindlar’s catalyst to form a cis alkene. This alkene is reacted with CH₂I₂and Zn(Cu) to form a cis-disubstituted cyclopropane ring.

Steps needed for carrying out the following synthesis

In the first step, 1-hexyne is converted to its sodium salt when it is treated with NaNH₂ in liquid ammonia. The sodium salt when treated with methylbromide yields 1-heptyne. This is followed by reduction with hydrogen in the presence of Lindlar’s catalyst to yield cis-1-heptene. When treated with CH₂I₂ in the presence of Zn-Cu, the methylene group adds to the double bond to yield a cis disubstituted cyclopropane ring as the product. The reaction can be given as:

Steps needed for carrying out the following synthesis