NMR assignments of a di‐pentacyclo‐undecane cyclic ether

Abstract

The X-ray structure of a di-pentacyclo-undecane cyclic ether was recently reported. As part of a programme to use NMR spectroscopy for the structure elucidation of cage compounds, the complete NMR assignments of the cyclic ether was attempted. Major overlap of proton and carbon signals of the two cages is observed. It was required to elucidate the fragment analogues that represent similar structural features of the cyclic ether in order to get an approximate but reasonable insight into the complex overlapping signals. Normal 2D NMR techniques were utilized to assign the various NMR signals.

Synthesis and NMR elucidation of novel penta‐cycloundecane amine derivatives as potential antituberculosis agents

“…However, based on the number of signals observed on the 1 H and 13 C spectra, it is clear that a conformational effect was again observed as reported before for other bi-dentate PCU analogous. [6,8] A total of two signals for each carbon on the homopiperazine moiety was observed on the 13 C, HMBC and HSQC spectra, this effect is caused by the restricted/hindered rotation of the amide group. [25,26] The methylene protons cis to the carboxamide oxygen will appear at a higher frequency compared to the transmethylene protons due to a through space deshielding effect from the carbonyl oxygen atom.…”

NMR elucidation of a novel (S)‐pentacyclo‐undecane bis‐(4‐phenyloxazoline) ligand and related derivatives

“…When the heteroatoms on the side arms are positioned in close proximity to the cage, it induces a through-space deshielding effect resulting in nonequivalence of atoms on the cage and that of the 'arm' similar to observations in previous reports of related chiral PCU ligands. [9,11] The infrared (IR) spectrum of 1 displays a sharp N-H absorption at 3312 cm −1 , and methyl absorptions at 2949 and 2929 cm −1 ; the absorption at 1646 cm −1 confirms the presence of the amide bond. The mass spectrum of 1 exhibits the correct molecular ion peak at m/z 741.4118 ([M + H] + ).…”

“…The PCU dione 6 was converted to the 3,5-diallyl-4-oxahexacyclo[5.4.1.0 2,6 .0 3,10 .0 5,9 .0 8,11 ]dodecane 7 as described previously. [15,16] This diene 7 is an intermediate in the synthesis of all the derivatives 1-5 being investigated.…”

NMR elucidation of some ligands derived from the pentacycloundecane skeleton

“…Synthesis of pentacyclo-[5.4.0.0 2,6 .0 3,10 .0 5,9 ]-undecane-8,11-dione-mono-ethylene ketal (5) [13] A mixture of the dione 4 (183.00 g, 1.05 mol), ethylene glycol (89.90 g, 1.45 mol), p-toluenesulphonic acid (6.11 g, 3.21 9 10 -2 mol) in dry benzene (800 mL) was gently refluxed with stirring in a Dean and Stark trap for 4 days. The reaction mixture was left to cool and poured slowly into ice-cold 10% (m/v) aqueous sodium carbonate (1 L).…”

“…2D NMR techniques have been used as an invaluable tool to overcome these difficulties. Our group has been actively involved in the elucidation of these cage compounds [7][8][9][10][11]. Novel compounds 1-3 were recently synthesized as part of an effort to develop new ligands for applications in asymmetric catalysis.…”