The monomethyl ester of azelaic acid was transformed into two fragments, namely [8-( methoxy -carbonyl) octyl ] triphenylphosphonium bromide and methyl 9-oxononanoate. A Wittig reaction between these two fragments produced dimethyl (Z)-octadec-9-enedioate and subsequent hydrolysis gave the title diacid. Interestingly, the same diacid was available directly from oleic acid in a published procedure which utilized a mutant strain of Candida tropicalis.