Stereoselective Synthesis of Enamides by Palladium Catalyzed Coupling of Amides with Electron Deficient Olefins

Abstract

A copper-free palladium-catalyzed convenient and efficient oxidative amidation protocol for synthesis of enamides by the cross-coupling of amides with acrylate has been developed. The thermodynamically disfavored Z-isomers are accessible by the intramolecular hydrogen bonding between the amido proton and carbonyl oxygen. The reactions were found to be acid catalyzed and p-TsOH gave the best result in enamide synthesis. The reactions were conducted at room temperature in presence of ambient air. This protocol has wide substrate scope allowing alkyl, aryl, substituted arylamides, urea, and its derivatives to react with methyl acrylate. The reactions are found to be tolerant to the steric demand of secondary amides and give the tertiary E-enamides in moderated to good yield.

Palladium‐Catalyzed Oxidative Sulfamidation: A Stereoselective Synthesis for Enesulfonamides

“…At the outset p ‐toluenesulfonamide ( 1a ) and n ‐butyl acrylate ( 2a ) were taken as model substrates to investigate the cross‐coupling possibility to achieve N ‐alkenylsulfonamides ( 3a ). Unfortunately, the use of similar conditions as reported previously by us, [i.e., Pd(OAc) 2 , BQ, p ‐TsOH in toluene] did not produce any trace of enesulfonamide (Table , entry 1) at room temperature with complete recovery of starting material over a period of 12 h. Raising the temperature to 70 °C leads to complete decomposition. However, replacement of the oxidant, benzoquinone (BQ) by Cu(OAc) 2 results in enesulfonamides in 18% yield (with Z:E =4:1).…”

Magnetically recyclable palladium nanoparticles (Fe3O4‐Pd) for oxidative coupling between amides and olefins at room temperature

“…Subsequently, Panda et al . reported the stereoselective synthesis of ( Z )‐enamides by coupling amides with electron‐deficient olefins employing 10 mol% palladium acetate as catalyst . However, use of homogeneous palladium catalysts in these enamide syntheses is associated with a number of disadvantages such as palladium metal contamination in the final product, use of co‐catalyst as well as non‐recoverability of the catalyst.…”

Dehydrogenative Heck Annelations of Internal Alkynes

“…In fact, palladium mono-or bistosylate is probably formed from palladium(II) acetate and p-toluenesulfonic acid as assumed by Panda and co-workers, who did not propose cationic intermediates for reactions catalyzed by such species. 21 Besides, protonation of the amide group by p-toluenesulfonic acid could take place; the balance between the N-and O-protonations would depend on the electron-withdrawing or -donating properties of the substituents, 22 hence the determining effect of the aryl substituent observed by the authors.…”