Syntheses of epoxides, and structural analysis of (E)[sbnd]N-hexyl-3-(trans-3-methyloxiran-2-yl)prop-2-enamide by spectroscopic techniques and DFT calculations

Abstract

Pyrethroids are three membered ring compounds similar to the natural pyrethrins produced by the flowers of Chrysanthemum cinerariaefolium and C. coccineum. Pyrethroids are insecticides and may also have insect repellent properties and are generally harmless to humans. Due to our interest in compounds with insecticidal activity, we have synthesized seven epoxides (2a-g), which are structurally similar to pyrethroids. The epoxides were prepared by stereospecific and regioselective epoxidation of seven dienamides (1a-g) with meta-chloroperbenzoic acid. The energies for two attainable epoxides (2g and 2g′) at their respective equilibrium geometries were calculated, and we have shown that the title epoxide (2g) is more stable than the candidate epoxide (2g′) (trans)N-hexyl-3-((E)-prop-1-en-1-yl)oxirane-2-carboxamide by 13.37 kJ mol−1. Experimental and calculated nuclear magnetic resonance chemical shifts were compared for both candidate epoxides (2g and 2g′), and a better match was achieved for the title compound (2g). The complementarity of Raman and infrared (IR) spectroscopies is a feature that can be explored for the characterization of this class of compound. This is shown by the bands around 3092 cm−1 in the Raman and absent in the IR spectra. On the other hand a strong peak at 1625 cm−1 in the IR is tiny in the Raman. Therefore the title compound was completely identified by NMR, IR, and Raman spectroscopies, and this protocol can be extended to the herein prepared epoxide analogues.