Knoevenagel condensations are especially important reactions for the synthesis of alkene compounds having electron-withdrawing groups such as COR,CN,COOR,NO2 etc. Recently,transition metal hydride ruthenium1, hydride and polyhydride rhenium2, and polyhydride iridium complexes have been found to be the efficient catalysts for Knoevenagle condensation. However the mentioned-above transition metal hydride complexes are not easily prepared. In addition, all of them are oxygen and H2O-sensitive, unstable compands. Therefor the catalytic reactions are required to be carried out under an inert atmosphere, and using the prepurified reagent.In the paper, We wish to report the development of Knoevenagel condensation catalyzed by ReBr(CO)5 under an air atmosphere in the absence of solvent.All the experiments were carried out under 1atm, without solvent.The resuIts of the representative Knoevenagel condensations are summarized in Table 1.The Knoevenagel reaction with diethyl malonate can be catalyzed by ReBr(CO)5, while the present Knoevenagel reactions catalyzed by transition metal have at least one cyano group in active methylene compouds.A propose mechanism for present catalytic coupling dehydration reactions is also illustrated in the paper.Briefly, this paper reports the ReBr(CO)5-catalyzed Knoevenagel reaction. The reaction is a new method for the Konevenagel condensation.