[1 + 2 + 3] Annulation as a General Access to Indolo[3,2- b]carbazoles: Synthesis of Malasseziazole C.

A formal [1 + 2 + 3] annulation of methyleneindolinones with o-alkenyl arylisocyanides has been developed for the general and efficient synthesis of both symmetrical and unsymmetrical indolo[3,2- b]carbazoles. The chemoselectivity of this domino reaction was tuned by a tethered alkenyl group, which enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology was used as a key step in the synthesis of the alkaloid malasseziazole C.

Formal [1 + 2 + 3] Annulation: Domino Access to Carbazoles and Indolocarbazole Alkaloids.

A new formal [1 + 2 + 3] annulation of o-alkenyl arylisocyanides with α, ß-unsaturated ketones under metal-, base-, and acid-free conditions is disclosed. This domino reaction provides a general protocol for the efficient and practical synthesis of a wide range of carbazole derivatives from readily available starting materials in a single operation. Furthermore, this methodology was used as the key step in a protecting-group-free synthesis of indolocarbazole alkaloids arcyriaflavin A and racemosin B.

Bicyclization of Azomethine Ylide: Access to Highly Functionalized 3H-Pyrrolo[2,3-c]quinolines.

A tandem bicyclization of azomethine ylides with methyleneaminochalcones was developed for the straightforward and facile synthesis of 2-substituted polyfunctionalized pyrrolo[2,3-c]quinolines. Both an unusual reactivity profile of azomethine ylide and a novel strategy for the construction of the tricyclic framework by the successive construction of the pyridine and pyrrole rings were exhibited in this domino reaction. Two intermediates are isolated in the control experiments, and thus a tandem bicyclization/elimination/oxidative aromatization process is proposed for the reaction mechanism.

Organocatalyzed aerobic oxidative Robinson-type annulation of 2-isocyanochalcones: expedient synthesis of phenanthridines.

A DBU-catalyzed aerobic oxidative Robinson annulation of 2-isocyanochalcones with active methylene ketones was developed for the expedient synthesis of phenanthridines in high to excellent yields. This unprecedented multistep domino reaction represents a new strategy for the construction of this tricyclic scaffold by the sequential formation of two rings and three C-C bonds in a single operation at room temperature.

Silver-Catalyzed Chemoselective [4+2] Annulation of Two Isocyanides: A General Route to Pyridone-Fused Carbo- and Heterocycles.

A silver-catalyzed chemoselective [4+2] annulation of aryl and heteroaryl isocyanides with α-substituted isocyanoacetamides was developed for the facile and efficient synthesis of 2-aminoquinolones, naphthyridines, and phenanthrolines. A mechanism for this multistep domino reaction is proposed on the basis of a 13 C-labeling experiment, according to which an unprecedented chemoselective heterodimerization of two different isocyanides generates an α-amidoketenimine intermediate, which undergoes 1,3-amino migration to form an α-imidoylketene, followed by 6 π electrocyclization.

Cross-Cycloaddition of Two Different Isocyanides: Chemoselective Heterodimerization and [3+2]-Cyclization of 1,4-Diazabutatriene.

A new cross-cycloaddition reaction between a wide range of isocyanides and 2-isocyanochalcones (or analogues) was developed for the expeditious synthesis of pyrrolo[3,4-b]indoles under thermal conditions. On the basis of the experimental results and DFT calculations, a mechanism for this domino reaction is proposed involving chemoselective heterodimerization of two different isocyanides to form 1,4-diazabutatriene intermediates, followed by an intramolecular [3+2]-cycloaddition and 1,3-proton shift.