A convenient, four-component reaction of o-phenylenediamines,
isocyanides, and selenium powder catalyzed by a natural abundant copper/air
(O2) catalyst system has been developed, providing a highly
step and atom economical protocol for the synthesis of benzo[4,5]imidazo[2,1-c][1,2,4]selenadiazol-3-imine derivatives with excellent
yields and good functional group tolerance. This method enables the
construction of an imidazo[2,1-c][1,2,4]selenadiazol
ring, one N–Se bond, one C–Se bond, and three C–N
bonds in a single step with only water as the byproduct. Preliminary
mechanistic studies imply that the copper/air (O2)-catalyzed
cyclization proceeds via a selenium-centered radical intermediate.
Sodium-carbonate-promoted green and facile synthesis of
5-amino-1,2,4-thiadiazoles and 5-amino-1,2,4-selenadiazoles with
elemental sulfur and selenium, respectively, was developed. This method
was carried out with O2 in the air as the green oxidant, and it has
several advantages, including low cost, low toxicity, and stable sulfur
and selenium sources, high atom efficiency with water as the sole
byproduct, simple operation, and broad substrate scope. Preliminary
mechanistic studies indicate that the formation of 1,2,4-thiadiazole
ring and 1,2,4-selenadiazole ring undergoes different processes.
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