Casting light on synthetic, SC-XRD and quantum mechanical studies for 2,1-benzothiazine based bis-adducts

Abstract

A series of new bis-adducts, based on 2,1-benzothiazine 2,2-dioxide heterocyclic ring system were prepared. The precursor compound, 1-benzyl-2,1-benzothiazin-4(3H)one 2,2-dioxide was synthesized from methyl anthranilate through multistep reaction. It was reacted with various substituted benzaldehydes in the presence of triethylamine to get the titled series of bis-adducts. Among the series, 1-benzyl-3-((1-benzyl-4‑hydroxy-2,2-dioxido-1H-benzo[c][1,2]thiazin-3-yl) (4‑chloro phenyl) methyl)-1H-benzo[c][1,2]thiazin-4-olate 2,2-dioxide 6a was obtained in crystalline form as triethylammonium salt and was studied by XRD analysis. The compound was crystalized with triclinic crystal system where the α, β and γ angles are 103.374(5)°, 100.646(5)° and 111.736(6)° respectively. The structure elucidation of the synthesized compounds was carried out by NMR and MS techniques. The compound 6a was selected as representative molecule among a series of bis-adducts to understand electronic properties and structural parameters. For this, various sorts of DFT based analyses such as natural bond orbital (NBO), frontier molecular orbital (FMO), global reactivity parameters (GRPs), natural population analysis (NPA) and molecular electrostatic potential (MEP) of 6a were procured at ωB97XD level along with 6–31G(d,p) basis set. NBO approach provided perceptions regarding the stability and charge migration of 6a. Furthermore, 4.837 eV band gap of HOMO/LUMO was determined and the GRPs were also accomplished with the aid of FMO energies. The findings of GRPs and NBO analyses described the chemical stability of 6a. Color plotting scheme of MEP surfaces directed towards reactive sited of 6a in terms of nucleophilicity and electrophilicity.