The synthesis of the (R)-3-METHYLHEPTANOIC ACID 2 from ester 4. Starting from the right side, reduc
tion with LiAlH4 followed by Swern oxidation, allowed
to convert ester 4 into aldehyde 10, which underwent
Wittig olefination smoothly to provide alkene 11 in high
yield. Hydrogenation of the double bond and removal of
the MOM ether in 11 gave alcohol 12 whose newly ex
posed hydroxyl was employed to expand one carbon.
From 12, a three-step sequence involving sulfonylation
(TsCl in pyridine), cyano substitution (NaCN in DMSO)
and hydrolysis of nitrile (reflux in sulfuric acid/water)
gave the desired (R)-methylheptanoic acid 2 over three
steps in 83% yield. The enantiomer excess of 2 was
measured by its derivative 15 to be 95.6%.[1]
