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

Question: Propose a synthesis pathway for the following compounds starting from acetylene: (a) 4-Octyne, (b) 4-Octanone, (c) cis-4-Octene, (d) trans-4-Octene, (e) 4-Octanol, (f) meso-4,5-Octanediol. Answer: (a) 4-Octyne can be synthesized by converting acetylene to 1-bromopentyne, followed by Glaser coupling and final hydrogenation using Lindlar's catalyst. (b) 4-Octanone can be synthesized by first forming 4-octanol from 4-octyne, followed by oxidation using PCC or Swern oxidation. (c) cis-4-Octene can be synthesized by converting acetylene to 4-octyne, followed by partial hydrogenation using Lindlar's catalyst. (d) trans-4-Octene can be synthesized by converting acetylene to 4-octyne, followed by partial hydrogenation using sodium metal in liquid ammonia. (e) 4-Octanol can be synthesized by converting acetylene to 4-octyne, followed by a hydroboration-oxidation reaction using diborane and H2O2/NaOH. (f) meso-4,5-Octanediol can be synthesized by forming 4-octene from acetylene and then performing a Sharpless asymmetric dihydroxylation using OsO4 and NMO as the catalyst.

Step-by-step solution

Formation of 1-heptyne from acetylene

First, we can convert acetylene to 1-bromopentyne by performing an alkyne nucleophilic substitution with n-butyllithium (n-BuLi), followed by a reaction with carbon tetrachloride (CCl4). Then, we can perform an alkyne coupling reaction called Glaser coupling using copper(I) chloride (CuCl). This reaction will yield the desired 1,8-diheptyne. The final step is to hydrogenate the alkyne at the 4th carbon using Lindlar's catalyst (Pd/CaCO3) with quinoline, which will give us the desired product, 4-Octyne. (b) 4-Octanone

Formation of 4-octanol from 4-octyne

First, form 4-octanol from 4-octyne as described in the synthesis of 4-octanol (e). After 4-octanol has been synthesized, follow the steps below.

Oxidation of 4-octanol to 4-octanone

Next, oxidize the hydroxyl group to a carbonyl group. This can be done using PCC (pyridinium chlorochromate) or Swern oxidation (DMSO and oxalyl chloride). This will yield the desired 4-Octanone. (c) cis-4-Octene

Formation of 4-octyne from acetylene

Form 4-octyne from acetylene as described in the synthesis of 4-octyne (a). After 4-octyne has been synthesized, follow the steps below.

Partial hydrogenation of 4-octyne to cis-4-octene

Partially hydrogenate 4-octyne to form cis-4-octene using Lindlar's catalyst (Pd/CaCO3) with quinoline. This will yield the desired cis-4-Octene. (d) trans-4-Octene

Formation of 4-octyne from acetylene

Form 4-octyne from acetylene as described in the synthesis of 4-octyne (a). After 4-octyne has been synthesized, follow the steps below.

Partial hydrogenation of 4-octyne to trans-4-octene

Partially hydrogenate 4-octyne to form trans-4-octene using sodium metal in liquid ammonia. This will yield the desired trans-4-Octene. (e) 4-Octanol

Formation of 4-octyne from acetylene

Form 4-octyne from acetylene as described in the synthesis of 4-octyne (a). After 4-octyne has been synthesized, follow the steps below.

Hydroboration-oxidation of 4-octyne to 4-octanol

Perform a hydroboration-oxidation reaction on 4-octyne using diborane (B2H6) followed by oxidation with H2O2 and NaOH. This will yield the desired 4-Octanol. (f) meso-4,5-Octanediol

Formation of 4-octene from acetylene

First, form either cis-4-octene or trans-4-octene from acetylene as described in the syntheses of cis-4-octene (c) or trans-4-octene (d). After 4-octene has been synthesized, follow the steps below.

Dihydroxylation of 4-octene to meso-4,5-octanediol

Perform a dihydroxylation reaction on 4-octene using a Sharpless asymmetric dihydroxylation with osmium tetroxide (OsO4) and N-methylmorpholine N-oxide (NMO) as the catalyst. This reaction will produce the desired meso-4,5-Octanediol.