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Unlike their ortho counterparts, meta-and para-acetamidoanilines can be converted into the corresponding acetamidoarenediazonium salts. These offer various opportuni-

exo-Methylene-β-lactams were synthesized in two steps from commercially available 3-bromo-2-(bromomethyl)propionic acid and reacted with arene diazonium salts in a Heck-type arylation in the presence of catalytic amounts of Pd(OAc) 2 under ligand-free conditions. The products, arylidene-βlactams, were obtained in high yields as single isomers. The βhydride elimination step of the Pd-catalyzed coupling reaction proceeds with high exo-regioselectivity and E-stereoselectivity. With aryl iodides, triflates, or bromides, the coupling products were isolated only in low yields, due to extensive decomposition of the starting material at elevated temperatures. This underlines that arene diazonium salts can be superior arylating reagents in Hecktype reactions and yield coupling products in synthetically useful yields and selectivities when conventional conditions fail.