Formation of N-coordinated 4H-benzo[d][1,3]oxazine from 2-(trimethylsiloxymethyl)- and 2-(hydroxymethyl)-phenyl isocyanides promoted by dirhodium(II) acetate

The neutral dirhodium(II) acetate [Rh-2(OAc)4] and the related cationic complex [Rh-2(OAc)2(MeCN)6](BF4)2 react with 2-(trimethylsiloxymethyl)phenyl isocyanide (I) and/or 2-(hydroxymethyl)phenyl isocyanide (II) to give the corresponding adducts, in which the entering isocyanide occupies the axial position at the two rhodium centres. These complexes are stable in toluene, but they evolve in chloroform as a consequence of an intramolecular ligand rearrangement via oxygen attack to the coordinated carbon atom. With the neutral dirhodium acetate species the cyclization reaction affords the well characterized benzoxazine complex (4), whereas the cationic acetonitrile derivative rapidly evolves into a complex mixture.