[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.

Catalytic Asymmetric [8+3] Annulation Reactions of Tropones or Azaheptafulvenes with meso‐Aziridines

“…Comparatively, azaheptafulvenes are usually applied as 8π components in [8+2] cycloadditions with electron‐deficient 2π‐components . A few examples of thermally allowed [8+3] cycloadditions have been realized to date . In 2008, Tomás’ group described the racemic annulation of Fisher alkenyl carbenes with azaheptafulvenes.…”

“…[8,9] Af ew examples of thermally allowed [8+ +3] cycloadditions have been realized to date. [10][11][12] In 2008, Tomµs' group described the racemic annulation of Fisher alkenyl carbenes with azaheptafulvenes. Recently,X u's group developed the [8+ +3] reactiono fN-sulfonyl 1,2,3-triazoles with azaheptafulvenes in the presence of rhodiums alts (Scheme 1b).…”

Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

“…Briefly, as a consequence of the interactions between cycloheptatrienyl and the metal ion, the nitrogen of 183 takes part in a 1,4 addition to carbene 182 to form endo metal conformation 186 . Finally, a cyclization provides the desired product 184 (Scheme 32B) [152] …”

Gold(I)‐Catalyzed [8+2]‐Cycloaddition of 8‐Aryl‐8‐azaheptafulvenes with Allenamides and Ynamides: Regioselective Synthesis of Dihydrocycloheptapyrrole Derivatives

“…The first studies on this transformation involved the use of electron‐deficient unsaturated systems as 2π partners; for instance, double‐activated styrenes [7] and cumulenes [8] (Figure 1 a). Later, it was described that the highly‐electrophilic alkenyl [5a] and alkynyl [9] Fisher carbene metal complexes can react as 2π component with high efficiency and selectivity (Figure 1 a).…”