Conformational analysis of bicyclo[3.3.1]nonane‐exo‐2,exo‐4‐dicarboxylic acid derivatives and related compounds

The stereoselective synthesis of esters 5a, 6, 7, 8, 12b, 12c, and 13 and dicarboxylic acids 5, 12, and 12a by KMnO4 oxidation, and, in the case of esters, diazomethane esterification, of the known tricyclic ketones 1, 2, 3, and 4 or their derivatives 9, 9a, 9b, 10, 10a, 11, and 11a, is described. Conformational analyses of these compounds have been carried out by 200‐MHz 1H‐NMR and 13C‐NMR spectroscopy at room temperature with the aid of theoretical calculations (MM2 program). Also, a 1H‐NMR study of compound 5a at temperatures between 21 and 119°C is presented. In general, a good agreement has been found among experimental and calculate average vicinal proton/proton coupling constant values. Compounds 5 and 5a, in [D6]DMSO and CDCl3 solutions, respectively, exist mainly as boat‐chair conformers, while compounds 6, 7, 8, and 13 exist mainly as chair conformers with respect to the bis(methoxycarbonyl)‐substituted cyclohexane or oxane ring. Compounds 12, 12a, 12b, and 12c show similar proportions for boat‐chair and chair‐chair conformers. Copyright © 1989 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim