Question: Each of the following syntheses requires more than one step. How

would you carry them out?

(a)

b)

Alkynes get converted to alkenes in the presence of hydrogen and Lindlar’s catalyst. The alkenes are further converted to alcohols by treating with ozone, zinc and ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$ .

(a)The given reaction shows the conversion of 1-pentyne to butanal. The reactant, 1-pentyne can be treated with${\mathrm{H}}_2$ and Lindlar’s catalyst to produce 1-pentene. This further reacts with${\mathrm{O}}_3$ , zinc and acetic acid to produce butanal. The reaction can be given as:

Alkynes are treated with ${\mathbf{NaNH}}_{\mathbf{2}}\mathbf{,}{\mathbf{NH}}_{\mathbf{3}}$ in the presence of alkyl bromide to give a higher alkyne. This further reacts with Li in ammonia to form the alkene.

(b)The reaction shows the conversion of 4-methyl-1-pentyne to trans-6-methyl-3-heptene.In the first step, the lower alkyne, 4-methyl-1-pentyne is converted to a higher alkyne, 6-methyl-hept-3-yne by reacting with${\mathrm{NaNH}}_2$ in liquid ammonia and${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}$ . The resultant alkyne further reacts with Li in ammonia to produce trans-6-methyl-3-heptene. The reaction can be given as: