A simple, convenient, and environmentally benign protocol for the synthesis of benzimidazoles from ortho-phenylenediamines and aldehydes via aerobic oxidation was developed in wet organic solvents. Notably, water significantly accelerated this transformation, which allowed us to achieve this important transformation without the assistance of any metal catalysts and other co-oxidants. Mechanistic studies suggested that water acts as the nucleophilic catalyst for this transformation by the conversion of disfavored 5-endo-trig cyclization of imines to favored 5-exo-tet cyclization via tetrahedral intermediates and the subsequent aerobic oxidation of the resulting benzimidazolines affords benzimidazoles.
Bibliographical noteFunding Information:
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government ( NRF-2013R1A1A1008434 and NRF-20100020209 ). C.-H.C. also thanks for a financial support from an NRF grant funded by the Korean Government ( NRF-2014-011165 , Center for New Directions in Organic Synthesis).
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- Aerobic oxidation
- Baldwin's rules
- Nucleophilic catalyst
ASJC Scopus subject areas
- Drug Discovery
- Organic Chemistry