Arene Ru (II)-catalyzed facile synthesis of N-acylhydrazones via acceptorless dehydrogenative coupling strategy

A facile catalytic one-pot synthesis of N-acylhydrazones via acceptorless dehydrogenative coupling of readily available alcohols and benzohydrazides (R2CONHNH2) using arene ruthenium (II) complexes has been described. The coupling of alcohols with various benzohydrazides using ruthenium catalysts provide a wide range of N-acylhydrazones in good to excellent yields (63-93%; 32 examples). The present protocol offers high selectivity of hydrazones without any alkylated products and tolerates a range of functional groups. Control experiments indicate that the mechanism proceeds via acceptorless dehydrogenation of alcohols, and hydrogen and water are the sole by-products. The gram scale synthesis illustrates the usefulness of the present strategy.