Synthesis of Succinimide Spiro-Fused Sultams from the Reaction of N-(Phenylsulfonyl)acetamides with Maleimides via C(sp2)-H Activation

Cascade [4 + 1] Annulation through Activation of the C(sp2)-H Bond Enabling Benzothiadiazinoisoindolcarboxylate, Benzothiadiazinoisoindole, and Benzothiadiazinoisoindolepyrrolidinedione as Hybrid Spiro-Heterocyclic Frameworks†

Two structurally distinct and biologically privileged succinimide and isoindole heteroarenes bearing benzothiadiazinedioxide motif-centered hybrid conjugates are proficiently achieved through Rh(III)-catalyzed sequential C(sp2)-H bond activation, ortho-alkenylation and finally cascade intramolecular cyclization. The significant feature of this developed protocol is that the resulting diversely decorated heterocycles contain a quaternary carbon center and this has been coursed through atypical [4 + 1] annulation ignoring the prevalent [4 + 2]-cyclization pathway and interestingly the applied coupling partners (e.g., maleimide, maleate, and styrene) to materialize the protocol functioned only as C1 synthon. Furthermore, the selective reduction strategy enables to modify the hybrid conjugate of succinimide and benzothiazine dioxide to benzothiazine dioxide-based spirocyclic isoindolopyrrolidinedione skeleton following preferential reduction of one carbonyl group of imide functionality. Overall this methodology emerges to be easily handled, versatile, time-efficient, and manifests relatively unfamiliar spiro-cyclization and good functional group tolerance so easy to grab a library of the entirely new variant of decorated hybrid spiro-heterocyclic scaffolds.

Recent advances in spirocyclization of maleimides via transition-metal catalyzed C-H activation

In recent years, the maleimide scaffold has received a great deal of attention in C-H activation. Several types of products can be constructed using maleimides as a coupling partner. Alkylation, alkenylation, annulation, dehydrogenative annulation and spirocyclization are various reactions shown by maleimides in C-H activation. Thus, the maleimide scaffold has been extensively studied in the last few years in C-H activation owing to its unique reactivity. Among the diverse class of reactions of maleimides, spirocyclization is a less explored reaction. The spirocycles, in particular the spirosuccinimides are interesting candidates in drug discovery and materials chemistry. Therefore the method of spirocyclization of maleimides via C-H activation becomes an important strategy for the synthesis of a diverse array of spirosuccinimides. This review summarizes the reports available in this field from 2015-2023 and also highlights the scopes and prospects of this method.

C-H activation-initiated spiroannulation reactions and their applications in the synthesis of spirocyclic compounds

Spirocyclic skeletons are prevalent in natural products, pharmaceuticals and organic functional materials. Meanwhile, transition-metal-catalyzed C-H activation reactions have demonstrated unparalleled advantages such as high efficiency, excellent atom-economy, good chemoselectivity and regioselectivity for the formation of target organic molecules. In recent years, C-H activation reactions have been creatively utilized in the synthesis of spirocyclic compounds. This review summarizes the most recent progress made in C-H activation-initiated spiroannulation reactions and their applications in the construction of structurally diverse and biologically valuable spirocyclic scaffolds by using alkynes, diazo compounds, maleimides, alkenes, quinones and cyclopropenones as the coupling partners.

Selective Construction of Spiro or Fused Heterocyclic Scaffolds via One-pot Cascade Reactions of 1-Arylpyrazolidinones with Maleimides

Presented herein is a controllable selective construction of spiro or fused heterocyclic scaffolds through the one-pot cascade reactions of 1-phenylpyrazolidinones with maleimides. To be specific, succinimide spiro pyrazolo[1,2-a]pyrazolones were effectively formed via [4 + 1] spiroannulation of 1-phenylpyrazolidinones with maleimides through simultaneous C(sp²)-H bond activation/functionalization and intramolecular cyclization along with the traceless fusion of the pyrazolidinonyl unit into the final product. In this reaction, air acts as a cost-effective and environmentally sustainable oxidant to assist the regeneration of the Rh(III) catalyst. Alternatively, succinimide-fused pyrazolidinonylcinnolines were formed from the same starting materials through an initial [4 + 1] spiroannulation followed by base-promoted skeleton rearrangement of the in situ formed spiro product without isolation. Notable features of these protocols include easily tunable selectivity, broad substrate scope, cost-effective and sustainable oxidant, excellent atom economy, and facile scalability.

Construction of C2-Quaternary-indol-3-ones via RhIII-Catalyzed [3+2] Spirocyclization from Indole Ketones and Nitroolefins

Novel complex C2-quaternary-indol-3-one units bearing versatile nitro groups have been successfully developed from pseudo-indolones and α,β-unsaturated nitroolefins through rhodium-catalyzed C-H activation/[3 + 2] spirocyclization. Notably, four diastereomers could be selectively obtained in the reaction by condition control.

Rh(iii)-catalyzed substrate-dependent oxidative (spiro)annulation of isoquinolones with diazonaphthoquinones: selective access to new spirocyclic and oxepine-fused polycyclic compounds

An efficient protocol for the selective synthesis of novel isoquinolone-containing spirocyclic and oxepine-fused polycyclic compounds via rhodium(iii)-catalyzed (spiro)annulation of NH-isoquinolones with diazonaphthalen-2(1H)-ones is reported.