Synthesis of 3-alkylideneisoindolin-1-ones via Sonogashira cyclocarbonylative reactions of 2-ethynylbenzamides.

Cyclocarbonylative Sonogashira reactions of ortho-ethynylbenzamides have been investigated. The process is carried out under CO pressure, in the presence of a very small amount of PdCl2(PPh3)2 (0.4 mol %) as a catalytic precursor, and without the need for a Cu salt as co-catalyst. 2-Ethynylbenzamide reacted successfully with iodoarenes bearing electron-withdrawing and electron-donating groups giving rise to different classes of compounds depending on the solvent used. On the contrary, N-(4-chlorophenyl)-2-ethynylbenzamide afforded exclusively polyfunctionalized isoindolinones with high stereoselectivity towards (E) isomers.