Efficient and scaleable methods for ω-functionalized nonanoic acids: Development of a novel process for azelaic and 9-aminononanoic acids (nylon-6,9 and nylon-9 precursors)

Article abstract of DOI:10.1021/op000081j

A new, convergent synthesis and process of the title open-chain C-9 compounds, valuable monomers for preparation of polyamides with specific properties, are discussed. Starting from relatively inexpensive raw materials, for example, cyclohexanone and activated C-3 olefins, the method provides polymer grade co-functionalized nonanoic acids. An improved protocol for cyanoethylation or carbalkoxyethylation of cyclohexanone in the presence of a catalytic amount of primary or secondary amines gave 3-(2-oxo-cyclohexane) propanecarboxylic acid derivatives 1 in high yield. Cyclohexaneperoxycarboxylic acid (CHPCA) is introduced as highly efficient reagent in Baeyer-Villiger rearrangement of 1. Pyrolysis of 2 (EWG = CN) afforded under optimized conditions 3 in high yield and regioisomeric purity, otherwise a mixture of three unsaturated isomeric ω-cyano nonenoic acids is obtained. Partial hydrogenation of unsaturated acids 3 allowed isolation of saturated long-chain difunctionalized acids 4. Hydrolysis of 4 led to 1,9-nonanedicarboxylic acid (azelaic acid) 5, whereas its hydrogenation at elevated pressure gave 9-aminononanoic acid 6. Alternatively, a practical four-step syntehsis of 5 via isolable 7-substituted oxepan-2-one (EWG = COOMe) 2 has been designed and experimentated. The versatile position of 3-(2-oxo-cyclohexane) propanecarboxylic acid derivatives 1 as raw materials for Fine Chemicals is also discussed.