- The idea to answer this question is to analyze the target molecule retro-synthetically by breaking a bond to the alpha carbon atom.
- Then we see the alkyl halide which needed as alkylating agent. The anion of diethyl malonate is a weaker base than ethoxide ion and reacts with secondary alkyl halides by substitution rather than elimination. Thus, the synthesis of 4-methyl hexanoic acid begins with the alkylation of the anion of diethyl malonate and 1-bromo- 2-methyl butane.
- Diethyl malonate has been alkylated with alkyl halide and the product converted to 4-methyl hexanoic acid by saponification, acidification and decarboxylation according to the following picture: