Conformational analysis of 14‐hydroxymodhephene by NMR, x‐ray diffraction and molecular modeling studies

Abstract

The conformational state of the [3.3.3]propellane framework for 14-hydroxymodhephene was determined by extensive application of one-and two-dimensional 1 H and 13 C NMR spectroscopy combined with x-ray diffraction studies of a synthesized derivative, spectral simulation and molecular modeling. The conformational rigidity of the molecule in solution, established at room temperature, revealed the existence of envelope conformers for both cyclopentane fragments, with C-7 puckered endo and C-10 exo with respect to the mean plane containing the B and C rings.

Conformational evaluation and detailed 1H and 13C NMR assignments of eremophilanolides

“…10 The published 1 H NMR spectrum was partially assigned, while the 13 C NMR assignments were correct, except for the C-14 and C-15 signals, which were interchanged. The 1 H NMR spectrum showed the signals corresponding to H(6) and H(8) overlapped, and the two signals of CH 2 2 seemed to have very similar chemical shifts and were partially overlapped with the signals of H(4), H(9ˇ), and Me (13), all this making their assignments difficult. However, acetylation of 5 to give 6 caused shifts of the H(4), H(6) and Me (13) signals.…”

“…The 1 H NMR spectrum showed the signals corresponding to H(6) and H(8) overlapped, and the two signals of CH 2 2 seemed to have very similar chemical shifts and were partially overlapped with the signals of H(4), H(9ˇ), and Me (13), all this making their assignments difficult. However, acetylation of 5 to give 6 caused shifts of the H(4), H(6) and Me (13) signals. This allowed an easy assignment and analysis of the coupling constant values of these signals, which was supported by gHSQC and gHMBC experiments and spectral simulation.…”

“…Typical 1D 1 H and 13 C spectra were acquired under standard conditions on Varian Mercury spectrometers operated at 300 and 75 MHz, respectively. 1 H spectra were obtained using a 4807.7 Hz spectral window with 16 384 data points, using Gaussian apodization for data processing, and 13 C spectra were obtained using a spectral window of 18 761.7 Hz with 131 072 data points for the processing. NOESY spectra were generated with a mixing time of 0.8 s, relaxation delay 1.0 s, data matrix 4K ð 4K (400 increments to 4 K, zero filling in F 1 , 4 K in F 2 ), 16 transients in each increments, spectral width 3000 Hz.…”

“…13 C NMR data have been reported for only a small number of these compounds. Therefore, and in continuation of our studies of sesquiterpenes, 12,13 we decided to perform the complete assignment of the 1 H and 13 C NMR spectra as well as a conformational evaluation of 1-6.…”

Wagner‐Meerwein rearrangement of a [3.3.3]‐ to a [4.3.3]propellane: deuterium tracer and conformational analysis

“…E-mail: smorales@cinvestav.mx conformational rigidity of the molecule in solution was established on the basis of NMR experimental and theoretical approaches. 7 In this work, we have investigated the Wagner-Meerwein rearrangement of protio and deuterated isotopomers of ( )-14-hydroxymodhephene (2) induced by p-tosylchloride. The 1 H and 13 C NMR assignments and conformational analysis of the resulting main product, ( )- [4.3.3]propellane 4, were established by the combined use of 2D NMR spectroscopy, deuterium isotopic effect on 13 C chemical shifts, DFT calculations and spectral simulation.…”