Question

Propose a synthesis of each compound starting from acetylene and any necessary organic and inorganic reagents. (a) 4 -Octyne (b) 4 -Octanone (c) cis-4-Octene (d) trans-4-Octene (e) 4-Octanol (f) meso- 4,5 -Octanediol

Short answer

Answer: H2, a dissolving metal (e.g., Na or Li), and liquid ammonia (NH3) can be used to selectively reduce the triple bond to a trans-double bond, resulting in trans-4-Octene.

Step-by-step solution

a) Synthesis of 4-Octyne

Step 1: Chain extension via acetylene nucleophilic addition: We start with acetylene and perform a nucleophilic addition reaction using a strong nucleophile (e.g., NaNH2) followed by an addition of 1-bromo-3-chloropropane. This will result in the formation of 4-pentyne. Step 2: Chain extension with a second acetylene: Perform another nucleophilic addition reaction with NaNH2 and acetylene, followed by the addition of 1-bromo-3-chloropropane. This will result in the formation of 4-octyne.

b) Synthesis of 4-Octanone

Step 1: Follow the steps for the synthesis of 4-octyne. Step 2: Ozoneolysis of 4-octyne: Treat 4-octyne with ozone (O3) and then hydrogen peroxide (H2O2) in a process called ozoneolysis. This will break the triple bond and convert it to a ketone, resulting in 4-octanone.

c) Synthesis of cis-4-Octene

Step 1: Follow the steps for the synthesis of 4-octyne. Step 2: Partial hydrogenation of 4-octyne: Hydrogenate the 4-octyne with H2 and Lindlar catalyst (or other similar catalyst) to selectively reduce the triple bond to a cis-double bond, resulting in cis-4-Octene.

d) Synthesis of trans-4-Octene

Step 1: Follow the steps for the synthesis of 4-octyne. Step 2: Partial hydrogenation of 4-octyne: Hydrogenate the 4-octyne with H2 and a dissolving metal (e.g., Na or Li) in liquid ammonia (NH3) in a process called dissolving metal reduction to selectively reduce the triple bond to a trans-double bond, resulting in trans-4-Octene.

e) Synthesis of 4-Octanol

Step 1: Follow the steps for the synthesis of 4-octyne. Step 2: Hydroboration-oxidation of 4-octyne: Perform a hydroboration-oxidation reaction with 9-BBN and hydrogen peroxide (H2O2) with a base (e.g., NaOH), which will reduce the triple bond to an alcohol group, resulting in 4-Octanol.

f) Synthesis of meso-4,5-Octanediol

Step 1: Follow the steps for the synthesis of 4-octyne. Step 2: Dihydroxylation of 4-octyne: Treat 4-octyne with OsO4 and N-methylmorpholine N-oxide (NMO) to perform a dihydroxylation reaction, which will add two hydroxyl groups to the carbon atoms involved in the triple bond. This results in the formation of meso-4,5-octanediol.