Synthesis of novel 1,2,4-oxadiazine derivatives and the substituent effect study on 13C NMR spectra

Abstract

In this study, eight mostly new 6-Methyl-4-phenyl-3-(substituted-phenyl)-4H-1,2,4-oxadiazin-5(6H)-one (OXA-ON) and eight new 6-Methyl-4-phenyl-3-(substituted-phenyl)-4H-1,2,4-oxadiazine-5(6H)-thione (OXA-TY) were synthesized. The synthesized heterocycle structures were characterized by IR, 1H NMR, 13C NMR and HRMS analyses. The carbons of interest in the OXA-ON and OXA-TY compounds are CH3, CH, C=N and C=O (C=S). The 13C NMR experimental chemical shifts (ppm) (SCS) of the CH3, CH, C=N, C=O (C=S) carbons of these OXA-ON and OXA-TY derivatives were correlated with the Hammett substitution constants and Swain-Lupton parameters, using the single substituent parameter (SSP) and dual substituent parameter (DSP) methods. Negative ρ values were detected for C=N and C=O carbons in OXA-ON derivatives and for C=N and C=S carbons in OXA-TY derivatives (reverse substituent effect). Positive ρ values were detected for CH carbon in OXA-ON derivatives and for CH3 and CH carbons in OXA-TY derivatives (normal substituent effect). According to the results of all statistical analyses, SCS (ppm) values of C=N, C=O carbons of OXA-ON derivatives, and C=N, C=S carbons of OXA-TY derivatives showed excellent correlation. The SCS (ppm) of CH carbon of OXA-ON and the CH3 and CH carbons of OXA-TY showed good correlation. The excellent and good correlations implied that the substituent effects are electronic in nature.