title: [8+2] and [8+3] cyclization reactions of alkenyl carbenes and 8-azaheptafulvenes: direct access to tetrahydro-1-azaazulene and cyclohepta[b]pyridinone derivatives.
abstract: The reactivity of Fischer alkenyl carbenes toward 8-azaheptafulvenes is examined. Alkenyl carbenes react with 8-azaheptafulvenes with complete regio- and stereoselectivity through formal [8+3] and [8+2] heterocyclization reactions, which show an unprecedented dependence on the C(beta) substituent at the alkenyl carbene complex. Thus, the formal [8+3] heterocyclization reaction is completely favored in carbene complexes that bear a coordinating moiety to give tetrahydrocyclohepta[b]pyridin-2-ones. Otherwise, alkenyl carbenes that lack appropriate coordinating groups undergo a formal [8+2] cyclization with 8-azaheptafulvenes to give compounds that bear a tetrahydroazaazulene structure. A likely mechanism for these reactions would follow well-established models and would involve a 1,4-addition/cyclization in the case of the [8+2] cyclization or a 1,2-addition/[1,2] shift-metal-promoted cyclization for the [8+3] reaction. The presence of a coordinating moiety in the carbene would favor the [1,2] metal shift through transition-state stabilization to lead to the [8+3] product. All these processes provide an entry into the tetrahydroazaazulene and cycloheptapyridone frameworks present in the structure of biologically active molecules.
authors: Instituto Universitario de Química Organometálica Enrique Moles, Unidad Asociada al CSIC, Universidad de Oviedo, Julián Clavería 8, 33006 Oviedo, Spain. barluenga@uniovi.es
authors: José
authors: J
authors: Barluenga
authors: Jaime
authors: J
authors: García-Rodríguez
authors: Silvia
authors: S
authors: Martínez
authors: Angel L
authors: AL
authors: Suárez-Sobrino
authors: Miguel
authors: M
authors: Tomás