Rh(III)-Catalyzed Oxidative Annulation of Isoquinolones with Diazoketoesters Featuring an in Situ Deacylation: Synthesis of Isoindoloisoquinolones and Their Transformation to Rosettacin Analogues

Transition Metal-Catalyzed C-H Activation/Annulation Approaches to Isoindolo[2,1-b]isoquinolin-5(7H)-ones

The isoindolo[2,1-b]isoquinolin-5(7H)-one scaffold is widely present in lots of bioactive natural products. Diverse types of strategies have been developed to construct this scaffold. Recently, transition metal-catalyzed C-H activation/annulation is emerging as a powerful and straightforward method to construct diverse polyheterocycles with high atom- and step-economy. It also has been employed for the synthesis of the isoindolo[2,1-b]isoquinolin-5(7H)-one scaffold. This review provides an introduction to recent advances for the preparation of isoindolo[2,1-b]isoquinolin-5(7H)-ones by using transition metal-catalyzed C-H activation/annulation. It will help researchers to find hidden opportunities and accelerate the discovery of novel transformations based on C-H activation/annulation.

Synthesis of Functionalized Isoquinolone Derivatives via Rh(III)-Catalyzed [4+2]-Annulation of Benzamides with Internal Acetylene-Containing α-CF3-α-Amino Carboxylates

A convenient pathway to a new series of α-CF3-substituted α-amino acid derivatives bearing pharmacophore isoquinolone core in their backbone has been developed. The method is based on [4+2]-annulation of N-(pivaloyloxy) aryl amides with orthogonally protected internal acetylene-containing α-amino carboxylates under Rh(III)-catalysis. The target annulation products can be easily transformed into valuable isoquinoline derivatives via a successive aromatization/cross-coupling operation.

Rhodium(III)-catalyzed oxidative annulation of isoquinolones with allyl alcohols: synthesis of isoindolo[2,1-b]isoquinolin-5(7H)-ones

An efficient rhodium(III)-catalyzed direct C-H oxidative annulation of isoquinolones with allyl alcohols as C1 synthons has been successfully developed. This protocol enables the straightforward synthesis of structurally diverse isoindolo[2,1-b]isoquinolin-5(7H)-ones with high atom economy, tolerates a broad spectrum of functionalities, and is applicable to one-pot operation from readily available N-methoxybenzamides.

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.

Accessing Extended Fused Isoindolinones Via Sequential Anionic Intramolecular Cyclizations

Sequential anionic intramolecular cyclizations and modelling were used for the first time to access unusual fused heterocyclic frameworks in excellent yields. 5-Exo-dig cyclizations yielded isoindolinone motifs and a subsequent 6-exo- and 7-endo-dig cyclization was directed to provide either fused isoquinoline or azepine frameworks. Regioselectivities were controlled by exploiting stereoelectronic effects via n_C- →π*_(Ph) interactions, and modelling studies provided reaction scope.

RhIII -Catalyzed C-H Activation of Aryl Hydroxamates for the Synthesis of Isoindolinones

RhIII -catalyzed C-H functionalization reaction yielding isoindolinones from aryl hydroxamates and ortho-substituted styrenes is reported. The reaction proceeds smoothly under mild conditions at room temperature, and tolerates a range of functional groups. Experimental and computational investigations support that the high regioselectivity observed for these substrates results from the presence of an ortho-substituent embedded in the styrene. The resulting isoindolinones are valuable building blocks for the synthesis of bioactive compounds. They provide easy access to the natural-product-like compounds, isoindolobenzazepines, in a one-pot two-step reaction. Selected isoindolinones inhibited Hedgehog (Hh)-dependent differentiation of multipotent murine mesenchymal progenitor stem cells into osteoblasts.

Construction of Bridged Carbocycles and Heterocycles via Rh(III)-Catalyzed C-H Alkylation/Michael Addition of 2-Arylindoles with Quinone Monoacetals

A rhodium-catalyzed formal [4 + 5] annulation reaction of 2-arylindoles with quinone monoacetals for the selective preparation of bridged nine-membered carbocyclic and heterocyclic compounds is developed. When 2-aryl substituted indoles are employed, this annulation reaction affords bridged nine-membered carbocyclic compounds with excellent indolyl C3 selectivity. On the other hand, with 2-aryl-3-substituted indoles as the substrates, bridged nine-membered heterocyclic compounds are exclusively formed via N1 annulation. Further transformations of the obtained products into new bridged compounds showcase the synthetic potential of this protocol.

Access to 5H-benzo[a]carbazol-6-ols and benzo[6,7]cyclohepta[1,2-b]indol-6-ols via rhodium-catalyzed C–H activation/carbenoid insertion/aldol-type cyclization

The rhodium-catalyzed mono-ortho C–H activation/carbenoid insertion/aldol-type cyclization of 3-aldehyde-2-phenyl-1H-indoles with diazo compounds has been developed.

Synthesis of polysubstituted quinolines through promoter-regulated selective annulation and C–C bond cleavage from 2-styrylanilines and β-keto esters

I₂ and Mn(OAc)₃ regulated annulation of 2-styrylanilines and β-keto esters is accomplished for chemoselective synthesis of 2-alkylquinolines and quinoline-2-carboxylates.

Copper and palladium-catalyzed sequential reactions: one-pot synthesis of isoindolo[2,1-b]isoquinolin-7(5H)-ones

A highly efficient protocol has been developed for the synthesis of diversely substituted isoindolo[2,1-b]isoquinolin-7(5H)-ones through sequential Cu(ii)-catalyzed Sonogashira coupling, intramolecular hydroamidation followed by palladium-catalyzed ligand-free Heck reaction. Good to excellent yields (41-94%) were observed with excellent substrate scope and functional group tolerance. The developed method represents a practical strategy for the construction of bioactive isoindolo[2,1-b]isoquinolin-7(5H)-ones.

Rhodium-Catalyzed Selective Oxidative (Spiro)annulation of 2-Arylindoles by Using Benzoquinone as a C2 or C1 Synthon

Rhodium-catalyzed substrate-tunable oxidative annulation and spiroannulation reactions of 2-arylindoles with benzoquinone leading to 9H-dibenzo[a,c]carbazol-3-ols and new spirocyclic products are reported. Intriguingly, with 2-aryl-substituted indoles, benzoquinone could act as a C2 synthon to afford dibenzo[a,c]carbazoles. On the contrary, when 2-aryl-3-substituted indoles were used, benzoquinone switched to act as a C1 synthon to furnish spirocyclic compounds. In addition, further transformations of the obtained products demonstrate the synthetic utility of the present protocol.

Rh-Catalyzed tandem C-C/C-N bond formation of quinoxalines with alkynes leading to heterocyclic ammonium salts

An efficient Rh-catalyzed oxidative C-H activation/annulation of 2-arylquinoxalines with internal alkynes is described using Cu(OAc)2·H2O and AgBF4 to afford a diverse variety of substituted quarternary ammonium salts at room temperature. The mechanism of the protocol is established on the basis of isolation of the 5-membered rhodacycle intermediate and kinetic isotope studies. The mild reaction conditions, substrate scope and functional group diversity are the salient practical features.