Ir(III)-Catalyzed Dual C-H Activation of 2-Aryl Phthalazinediones and 3-Aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides for the Construction of Spiro-Fused Cyclic Frameworks

Ru(II)-catalyzed oxidative C-H spiroannulation of 4-arylquinazolin-2-ones with alkynes

A novel strategy has been devised for the synthesis of spiro[indene-1,4'-quinazolin]-2'(3'H)-one frameworks through Ru(II)-catalyzed tandem ortho-C-H bond activation and spiroannulation of 4-arylquinazolin-2-ones with alkynes. This is the first example of spiroannulation of 4-arylquinazolin-2-ones with internal alkynes. It is a versatile approach for synthesizing spiro[indene-1,4'-quinazolin]-2'(3'H)-one scaffolds with a broad substrate scope and high functional group tolerance.

Rh(III)-Catalyzed Sequential ortho-C-H Bond Annulation and Desulfonylation of 3-Aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides: Access to 1-Aminoisoquinolines

An efficient Rh(III)-catalyzed C-H functionalization of 3-aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides with diaryl and dialkyl alkynes has been developed for the first time to the synthesis of 1-aminoisoquinoline derivatives in a single step. This method involves through the formation of one C-C bond and one C-N bond followed by desulfonylation to generate a novel series of isoquinolines in good to excellent yields. This is a direct method to produce pharmaceutically more relevant scaffolds with a high functional diversity.

Rhodium-Catalyzed Functionalization and Annulation of N-Aryl Phthalazinediones with Allyl Alcohols

A direct ortho-Csp2-H acylalkylation of 2-aryl-2,3-dihydrophthalazine-1,4-diones with unsubstituted and substituted allyl alcohols is achieved in high yields through Rh(III)-catalyzed C-H bond activation process. The additional employment of Cu(OAc)2⋅2H2O as an oxidant detour the reaction towards [4+1] annulation, producing 13-(2-oxopropyl)-13H-indazolo[1,2-b]phthalazine-6,11-diones in moderate yields. Interestingly, Lawesson's reagent-mediated conditions accomplished intramolecular cyclization in ortho-(formylalkylated)-2,3-dihydrophthalazine-1,4-diones to produce diazepino[1,2-b]phthalazine-diones in moderate yields. Furthermore, allyl alcohol showcased distinct reactivity in presence of different additives to produce ortho-allylated, oxidative and non-oxidative [4+2] annulated products.

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.

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.

Rh(III)-catalyzed [3 + 2] spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates through ortho-C-H bond functionalization

Rhodium(III)-catalyzed [3 + 2]-spiroannulation of 2-aryl-1,4-benzoxazines with 4-hydroxy-2-alkynoates has been developed for the synthesis of highly rigid spirolactones in good yields with high regioselectivity. The reaction proceeds through a cascade of C-H activation followed by C-H annulation and lactonization. In this approach, two C-C and C-O bonds are formed in a single step. This is the first report on the spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates.