Studies on Synthesis of 10, 11-Dihydro-5H-dibenzo[a, d]cycloheptene Derivatives, III. : Stereostructures of Isomeric 8, 9-Dimethoxycarbonyldibenzo[2, 3 : 5, 6]bicyclo[5.2.0]nonan-4-ones Determined by ¹H-¹H and ¹³C-{¹H}Nuclear Overhauser Effects in Nuclear Magnetic Resonance Spectroscopy

Abstract

Stereochemistry of 8, 9-dimethoxycarbonyldibenzo[2, 3 : 5, 6]bycyclo[5.2.0]nonan-4-ones (2a, 3a, 4a, and 5a) and 8, 9-dimethoxycarbonyl-4-hydroxydibenzo[2, 3 : 5, 6]tricyclo[5.2.0.0^4.8]nonanes (6a and 7a) was studied by chemical and spectrometrical means.Intramolecular acid anhydride formation reactions of isomeric cis-dicarboxylic acids (3c, 5c, 6c, and 4c) afforded the anhydrides (3d, 5d, 6d, and 5d), respectively. Interconversion between 2a and 3a and between 4a and 5a at higher temperature by thermal reaction resulted in equilibria of 2a and 3a (3 : 2) and of 4a and 5a (20 : 1).Detailed ¹³C and ¹H assignments (3a, 4a, 5a, 6a, and 7a), and stereostructural assignments (3a, 4a, and 5a) were made by using nuclear magnetic resonance (NMR) techniques such as ¹H-{¹H} and ¹³C-{¹H}NMR, ¹³C/¹H chemical shift-correlated NMR, and ¹H-¹H and <13>C-{¹H} nuclear Overhauser effect (NOE) measurements. Moreover, a possible mechanism of interconversion between 4a and 5a is discussed.