Question

Which of the given sequences helps convert pentane-1,5-dioic acid to heptane-1,7-dioic acid?

• A. 1: $\text{Na-Hg}\text{amalgam}$;
  2: $PB{r}_3$;
  3: $\text{KCN}\text{followed by}{H}_3{O}^{+}$
• B. 1: $NaB{H}_4$ in acid;
  2: $PB{r}_3$;
  3: $\text{KCN}\text{followed by}{H}_3{O}^{+}$
• C. 1: $LiAl{H}_4$ followed by work up;
  2: $PB{r}_3$;
  3: $\text{KCN}\text{followed by}{H}_3{O}^{+}$
• D. None of the above

Answer 1

The correct option is C

1: $LiAl{H}_4$ followed by work up;
2: $PB{r}_3$;
3: $\text{KCN}\text{followed by}{H}_3{O}^{+}$

Start by reducing glutaric acid into its corresponding diol using LAH reduction and workup:

The diol is converted to its corresponding dibromoalkane using $PB{r}_3$.
The bromide groups are displaced by cyanide via substitution.
The dinitrile on hydrolysis yields the required heptanedioic acid: