A Cobalt Mediated Nitrene Transfer aza-Wittig Cascade Reaction To Access 1,3,4-Oxadiazole Scaffolds
Daniël S Verdoorn1,2, Prabhat Ranjan2, Tim de Reuver2
1Division of Organic Synthesis, Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Abstract:
A cobalt(II) mediated three-component synthesis of 5-substituted-N-sulfonyl-1,3,4-oxadiazol-2(3H)-imines using sulfonyl azides, N-isocyaniminotriphenylphosphorane (NIITP), and carboxylic acids has been developed. This one-pot tandem reaction starts with a nitrene transfer to NIITP, followed by addition of the carboxylic acid to the in situ formed carbodiimide and subsequent intramolecular aza-Wittig reaction. Both the steric constraints of carboxylic acid and the stoichiometry of the employed cobalt salt determine the selectivity toward the two products, i.e. 5-substituted-N-sulfonyl-1,3,4-oxadiazol-2(3H)-imine versus 5-substituted-4-tosyl-2,4-dihydro-3H-1,2,4-triazol-3-one.
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