title: Unexpected reaction pathways in the reaction of alkoxyalkynylchromium(0) carbenes with aromatic dinucleophiles.
abstract: Thermal- or SiO(2)-induced reactions of the Michael adducts of 1,2-aromatic dinucleophiles and alkynylchromium(0) carbene complexes, compounds 7-10, form different products in good yields depending on the nature of the aromatic dinucleophile used. Thus, 1,2-diaminobenzene derivatives 7 and 8 rearrange to pentacarbonylchromium(0) isocyanide complexes 11, 12, 14, and 15 in a process that occurs through bicyclic intermediates 24. Adducts 9 derived from o-aminophenol give 2,3-dihydro-1,5-benzoxazepine derivatives 17 by intramolecular 1,2-addition, followed by protonation at the chromium center and reductive elimination. In contrast, base-promoted addition of the phenolic hydroxy group in compound 9 a affords 3-ethoxy-5-phenyl-5,6-dihydro-2H-1,6-benzoxazocin-2-one (18), together with the expected adduct 17 a. Compound 18 is formed by a nucleophilic addition to a CO ligand in a preformed carbene complex. This is a new example of the rare attack of a nucleophile on a CO ligand in a Fischer carbene complex. Adducts 10 form seven-membered-ring carbene complexes 19 and 20 by intramolecular aminolysis. In contrast, reaction of alkynyl carbene complexes with 1,8-diaminonaphthalene under very mild conditions leads to 2-substituted perimidines 33 together with the corresponding ethoxymethylmetal carbene complex 32 through an unprecedented fragmentation process in a formal retro-Aumann reaction.
authors.affiliation: Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain. sierraor@quim.ucm.es
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Sierra
authors.forename: María J
authors.initials: MJ
authors.lastname: Mancheño
authors.forename: Juan C
authors.initials: JC
authors.lastname: del Amo
authors.forename: Israel
authors.initials: I
authors.lastname: Fernández
authors.forename: Mar
authors.initials: M
authors.lastname: Gómez-Gallego