An exception to the normal Mitsunobu reaction with phenols; the formation of hydrazones from salicylaldehydes

The reaction of 2-hydroxybenzaldehydes with alkanols in the presence of triphenylphosphine and di-tert-butyl azodicarboxylate (DBAD), under the Mitsunobu reaction conditions, gives rise to the formation of hydrazones as the major products rather than the expected alkyl aryl ethers.