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 thein situformed carbodiimide
and subsequent intramolecularaza-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.