Construction of a Clock Catalytic System: Highly Efficient and Self-Indicating Synthesis of Benzoheterocycles at Ambient Temperature

Inspired by the mechanism of the clock reaction, we rationally constructed a novel phosphomolybdenum blue (PMB) clock catalytic system for a highly efficient synthesis of benzimidazoles and benzothiazoles simply at ambient temperature. The current PMB clock catalytic system exhibits a sharp decoloration event to announce the depletion of the intermediateconstraint, making this synthetic approach self-indicating and TLC-free.P-31 NMR and XPS analysis of PMBcatalyst showed that only two Mo6+ atoms are reduced to Mo5+ atoms in the Keggin structure due to the moderate reducibility of benzimidazoline and benzothiazoline intermediates. Thus,the active Keggin-type POM cluster could be well maintained in DMSO during the redox cycling of phosphomolybdic acid (PMA) and PMB. H-1 NMR tracing experiment not only confirmed the proposed reaction mechanism but also showed that PMB exerts Lewis acid catalytic activityat the early phase of the reaction other than the expected redox catalytic activity.

Automated summary

This research developed a novel phosphomolybdenum blue clock catalytic system for the efficient synthesis of benzimidazoles and benzothiazoles at ambient temperature, with self-indicating properties. Through various NMR and XPS analyses, the structure and reactivity of the PMB catalyst were investigated.