Synthesis and Comprehensive Structural and Chiroptical Characterization of Enones Derived from (−)-α-Santonin by Experiment and Theory

Abstract

The aim of the present work is to explain the causes of the observed deviations from sector and helicity rules to determine the absolute configuration of optically active α,β-unsaturated ketones by means of electronic circular dichroism (ECD). To this end, a series of model compounds with a common decahydronaphthalene skeleton representing both cisoid and transoid enones were synthesized. In the framework of this work, detailed dichroic studies supported by single crystal X-ray analysis were performed where possible. To assist the achievement of the desired objectives the conformational flexibility of the selected cis-enones through the dependence of solvent and temperature on the ECD spectra were examined. All experimental studies were supplemented by detailed DFT calculations. A notable result of the study is assessing the applicability of the enone sector and helicity rules in dichroic studies and potential restrictions. To this end, a number of factors that could determine the signs of the individual Cotton effects has been considered. Among these nonminimum structure effects, i.e., twisting of the enone chromophore and nonplanarity of the enone double bond can be mentioned.

Reassignment of the absolute configuration of plakinidone from the sponge consortium Plakortis halichondrioides–Xestospongia deweerdtae using a combination of synthesis and a chiroptical approach

“…39,40 This also holds true in the case of the studied molecule. Comparison of the ECD spectra of individual conformers shows that there is no characteristic band (with the unchanged position and sign), which could be used for the C17 center configuration assignment (Figs.…”

Epigenetic Manipulation to Trigger Production of Guaiane-Type Sesquiterpenes from a Marine-Derived Spiromastix sp. Fungus with Antineuroinflammatory Effects

“…The NOE interaction between H 3 -12 (δ H 1.24, d, J = 6.8 Hz) and H-2 reflected both H-2 and H-4 in a trans orientation. Based on the enone helicity rule, 22 the negative Cotton effect (CE) at 340 nm and the positive CE at 250 nm were attributed to n → π* and π → π* transitions of the enone chromophore (Figure 3c) for an M-type enone torsion angle, implying the existence of the 2S configuration. This assignment was in agreement with the computed ECD data for a model molecule without methyl substitution at C-4 but with (2S)-OH (Figure S86l.…”

“…This data suggested that both H-2 and H-4 were on the same face, differing from 3 . According to the enone helicity rule, the positive CE at 340 nm and negative CE at 250 nm for n → π* and π → π* transitions in 4 (Figure d) agreed with a P -type helicity of the enone torsion angle, suggesting the existence of the 2 R configuration. The Mitsunobu reaction allowed the conversion of 4 to 3 , supporting 4 as the 2-epimer of 3 .…”

Extended tight‐binding quantum chemistry methods

“…Previous studies have shown that for some optical properties, MD sampling is essential 29,40,44,167–169 . Here, an MD simulation is performed, and snapshots are taken equidistantly from the resulting trajectory.…”