) 4 ]/NaY} catalyst was applied successfully to the Heck arylation of acrolein diethyl acetal using a large variety of aryl and heteroaryl bromides. Depending on the reaction conditions (Heck versus Cacchi) good to high selectivities toward the 3-arylpropionic esters or to the cinnamaldehydes were achieved, respectively. Under classical Heck conditions, while the catalyst was found to be stable over the two first runs, it showed significant loss of activity from the third cycle. Under Cacchi conditions, the catalyst could not be reused as it led to high dehalogenation rates. All results indicate that the reactions proceed through dissolved palladium species in the bulk solution (leaching). As observed by transmission electronic microscopic (TEM) analyses, while these species can be trapped and stabilised by the zeolite framework under the Heck conditions, they tend to form large palladium(0) aggregates under the Cacchi conditions leading to dehalogenation rather than to the expected Heck coupling.

Efficient Heterogeneously Palladium-Catalyzed Heck Arylation of Acrolein Diethyl Acetal. Selective Synthesis of Cinnamaldehydes or 3-Arylpropionic Esters.-The heterogeneous complex Pd(NH3)4 on zeolite NaY represents a viable alternative to the homogeneous Pd catalysts in Heck arylation of acrolein diethyl acetal. The reaction provides a wide range of cinnamaldehydes (IV) or arylpropionic acid esters (III), selectively, depending on the use of Cacchi or standard Heck conditions, respectively. Under Heck conditions, the catalyst can be reused for two consecutive runs while no recycling is possible under Cacchi conditions due to increased side product formation. -(NOEL, S.; LUO, C.; PINEL, C.; DJAKOVITCH*, L.; Adv. Synth. Catal. 349 (2007) 7, 1128-1140; Inst. Rech. Catal. Environ., CNRS, Univ. Claude Bernard Lyon, F-69626 Villeurbanne, Fr.; Eng.) -Mischke 36-037