Palladium-Catalyzed Intramolecular Cyclization: Access to Rare PentacyclicN-Fused Heterocycles

Abstract

Herein, we report a rare pentacyclic N‐fused hetrocycle synthesis via palladium catalyzed intramolecular C−H arylation along with the brief synthetic study of new type of bicyclic/tricyclic pyrrole rings. This pyrrole rings provided diversely substituted polycyclic nitrogen fused heterocycles from N‐benzyl/N‐benzyloxy pyrroles with good to excellent yields.

[3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-b][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-b][1,2]oxazine Derivatives

“…The literature provides limited data on the preparation of pyrrolo[1,2- b ]oxazine derivatives [ 78 , 79 ], especially possessing an unsaturated pyrrole core [ 80 , 81 ]. Therefore, we elucidated the scope of the found transformation.…”

Recent synthetic journey on pyrrole-fused compounds

“…We proposed a general mechanistic pathway for heteroarylation, which proceeded via oxidative addition, followed by intramolecular C-H activation in the presence of Pd-catalyst. 28 The Pd-catalyzed cyclization precursor 48 contains a -Br atom for oxidative addition and the substrate scope becomes broader if the -Br atom is replaced by an -H atom via oxidative intramolecular cyclization. Under suitable reaction conditions, the precursor has greater scope for sp 3 C-H activation (a to the ester carbon) vs. sp 2 C-H activation (heteroaryl ring).…”

“…Furthermore, the aldehyde Scheme 13 Synthesis of pentacyclic N-fused heterocycles via Pd-catalyzed heteroarylation. 28 of the aromatic ring with a higher electron density yielded less of the required product. In contrast, the ketone group failed when reacted with the mild acid AcOH in the Pictet-Spengler reaction, whereas was successful with the strong acid TFA.…”

“…We proposed a general mechanistic pathway for heteroarylation, which proceeded via oxidative addition, followed by intramolecular C–H activation in the presence of Pd-catalyst. 28…”

6-Exo-dig cyclization/dearomatization cascade towards N–O fused spiro polyheterocycles

“…[30][31][32] Meanwhile, a protocol based on dearomatization for the efficient construction of structurally novel N-O fused spiro polyheterocycles has rarely been explored. [33][34][35] As a result of the significance of metal-free approaches in academia and industry, as well as our continuing interest in the preparation of novel polyheterocycles, [36][37][38][39][40] we herein develop a metal-free tandem cyclization of N-alkoxybenzamides for the synthesis of diverse N-O fused spiro polyheterocycles by employing a hypervalent iodine(III) reagent (Scheme 1c).…”