Synthesis of 2‐Imino‐1,3,4‐Selenadiazoles via Tributylphosphine‐Mediated Annulation of N‐Aroyldiazenes with Isoselenocyanates

Abstract

2-Imino-1,3,4-selenadiazole derivatives can be synthesized from hydrazides and isoselenocyanates by sequential oxidation and a tributylphosphine (PBu 3 )-promoted annulation reaction at room temperature. In this synthetic process, crude less stable N-aroyldiazene intermediates generated by I 2mediated oxidation of hydrazides were used directly in a subsequent annulation reaction to afford the selenadiazole products. The merits of the present synthetic strategy also include absence of transition metals and gram-scale synthesis.

Elemental Sulfur Promoted Cyclization of Aryl Hydrazones and Aryl Isothiocyanates Yielding 2-Imino-1,3,4-thiadiazoles

“…A nearly identical approach could be used to afford 2-imino-1,3,4-selenadiazoles, using P(nBu) 3 . 6 Notably, those phosphorus-containing compounds should raise concerns regarding storage conditions and cost effectiveness. 7 As such, upcoming methods are still expected as they would provide more convenient options to afford 2-imino-1,3,4thiadiazoles.…”

“… Hydrazines were oxidized in the presence of molecular iodine to furnish N -acyldiazenes, which then underwent a P­(NMe 2 ) 3 -promoted cyclization with aryl isothiocyanates. A nearly identical approach could be used to afford 2-imino-1,3,4-selenadiazoles, using P­( n Bu) 3 . Notably, those phosphorus-containing compounds should raise concerns regarding storage conditions and cost effectiveness .…”