Ring opening and closing in heterocyclic compounds. 1H nuclear magnetic resonance studies on the reaction between 6-nitrobenzothiazole and methoxide ion in dimethyl sulphoxide–methanol

Abstract

The reversible interaction between 6-nitrobenzothiazole and methoxide ion in DMSO or DMSO–MeOH mixtures leads to the open anion 2-methoxymethyleneamino-5-nitrobenzenethiolate (III), via a Meisenheimer-like adduct. Addition of CH₃I or Br₂–pyridine in CCI₄ to the reaction mixtures yields 2-methoxymethyleneamino-5-nitrophenyl methyl sulphide or bis-(2-methoxymethyleneamino-5-nitrophenyl) disulphide respectively. ¹H N.m.r. studies show that in DMSO–MeOH rapid addition of MeOH to the NC double bond of (III) occurs.