Practical Synthesis of 1,1′-Binaphthyl-2-carboxylic Acids via Side Chain Oxidation of 2-Methyl-1,1′-binaphthyls

Four 1,1′-binaphthyl-2-carboxylic acids were obtained in 38–53% isolated yield via three-stage oxidation of 2-methyl-1,1′-binaphthyls, that is, i) NBS-bromination to benzylic bromides, ii) treatment with sodium salt of 2-nitropropane to aldehydes, and iii) KMnO4–oxidation to carboxylic acids.