Efficient synthesis of omega-functionalized nonanoic acids

Starting from cyclohexanone and acrylonitrile, a four-step synthesis of the title open-chain C-9 compounds is reported. An improved protocol for cyanoethylation of cyclohexanone in the presence of a catalytic amount of cyclohexylamine afforded 3-(2-oxocyclohexyl)-propanenitrile (1) in 92% yield. Cyclohexaneperoxycarboxylic acid (CHPCA) is introduced as a highly efficient reagent in the Baeyer-Villiger rearrangement of 1, yielding over 90% of 2. Pyrolysis of 2 afforded under optimized conditions 3 in 92% yield and 99% regioisomeric purity, otherwise a mixture of three unsaturated isomeric omega-cyano nonenoic acids 3, 10 and 11 is obtained. Partial hydrogenation of 3 allowed the isolation of 4 in 90% yield. Hydrogenation of 4 at elevated hydrogen pressure gave 9-aminononanoic acid (5), whereas hydrolysis of 4 led to 1,9-nonanedioic acid (azelaic acid, 6). Both, 5 and 6 are valuable C-9 monomers for the preparation of polyamides with specific properties.