Efficient Heterogeneously Palladium‐Catalysed Heck Arylation of Acrolein Diethyl Acetal. Selective Synthesis of Cinnamaldehydes or 3‐Arylpropionic Esters

Abstract

) 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.

Heck arylation of alkenes with aryl bromides by using supported Pd catalysts: a comparative study

“…The selectivity of the formation of the main product, transstilbene, was only decreased by the formation of minor amounts of cis-stilbene and 1,1-diphenylethylene. Most importantly, in contrast to previous reports, no dehalogenation and/or aryl-aryl coupling product was observed in any of the reactions [42].…”

Aqueous Heck Arylation of Acrolein Derivatives: The Role of Cyclodextrin as Additive

“…The recovery and the separation of the soluble palladium catalyst from the product need additional work-up procedures which are often expensive and lead to generation of large volumes of waste. A possible route to achieve an efficient C-C formation under mild conditions, which includes the choice of solvent, low catalyst loading, easy separation and recyclability of the catalyst, is the use of heterogeneous palladium catalysts [6,18,19]. In the literature, several reports described the possibility of using porous supports to immobilize palladium complexes or to support palladium particles for the Heck reaction, including active carbon and metal oxides.…”

“…Among all these chemicals, cinnamaldehyde derivatives and 3-aryl propionic acids are very common building blocks in organic synthesis [4,5]. We have extensively studied this reaction in organic solvents and more recently in aqueous solution, [6] since water emerges as a sustainable solvent and has several advantages such as low cost, abundance, easy separation from organic products [7,8]. However, the exclusive use of water often leads to modest yields and the use of phase transfer agent additives like tetraalkylammonium salts are essential in order to circumvent such limitation [9,10].…”

(2E)-3-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-2-propenal

“…These methods allowed also to prepare (hetero)aromatic 2,3-unsaturated aldehydes containing pyridine, chinoline, isoquinoline, thiophene and benzothiophene nuclei [6][7][8][9].…”

“…In recent years efficient protocols for the preparation of aromatic 2,3-unsaturated aldehydes by Heck type palladium catalyzed cross-coupling reactions of arylhalides with acrolein diethylacetal [6][7][8] or 3,3-diacetoxypropene [9] have been developed. These methods allowed also to prepare (hetero)aromatic 2,3-unsaturated aldehydes containing pyridine, chinoline, isoquinoline, thiophene and benzothiophene nuclei [6][7][8][9].As a result of our interest in the synthesis of functionalized pyrazoles [10-13], we have developed a synthetic pathway to (2E)-3-(1-phenyl-3-methoxy-1H-pyrazol-4-yl)-2-propenal as a precursor to biologically active compounds and materials for non-linear optics. …”