Palladium-catalyzed seven-membered N,O-heterocycle ring formation

3-Methyl-5-methylene-1,3-benzoxazepin-2-one (3) has been prepared starting from o-iodophenyl N-allyl-N-methylcarbamate in the presence of tetrakis(triphenylphosphine) palladium(0) as catalyst. The X-ray structure of the intermediate palladium complex (2), resulting from oxidative addition of the aromatic iodide to palladium, is reported. It consists of a square planar arrangement of aryl, iodide and two mutually cis triphenylphosphine ligands. The double bond being not coordinated to palladium, its insertion to generate the seven-membered ring almost quantitatively requires the use of thallium acetate in dimethylacetamide, otherwise intermolecular reactions predominate, leading to carbon-carbon bond formation between the aryl and double bond carbon of two and three substrate molecules, respectively, with formation, in the latter case, of a 24-membered ring. (C) 1998 Elsevier Science S.A.