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

Diastereoselective Cascade Double Michael Addition to Access Bridged Coumarins, Oxindoles and Spirooxindoles: A Sustainable Strategy for Synthesis of Anticancer Molecules

An efficient and concise synthesis of highly functionalized bridged coumarins has been developed through a diastereoselective double Michael addition reaction of p-quinols with various 4-hydroxy coumarins under catalyst-free conditions in H2O-DMSO (8 : 2). The method has been applied to oxindoles for the synthesis of a variety of bridged-oxindoles and bridged-spiroxindoles in presence of a DABCO base using H2O-EtOH (8 : 2) as solvent medium. The strategy is simple, highly atom economical as there is no by-product and environmentally benign (E-factor=0.1-0.9). The synthesized compounds were screened against triple-negative breast cancers and found that bridged coumarin (3 a) and oxindole (5 d) compounds exhibit potent anti-cancer activity at 6.6 and 8.8 μM (IC50) concentrations respectively. Further analysis revealed that 3 a and 5 d caused elevated early and total apoptosis by arresting the MDA-MB-468 cells in G2/M phase of the cell cycle. Overall, our results demonstrate that bridged coumarin (3 a) and oxindole (5 d) compounds-based approach attenuates the cancer progression and may pave a path for the translational outcome.

Iron-Catalyzed Reductive Ring-Rearrangement Reaction of Bridged Benzo[b]oxocin-4-ones with Grignard Reagents to Afford Bridged Benzo[b]oxocin-2-ols

An iron-catalyzed reductive ring-rearrangement reaction of bridged benzo[b]oxocin-4-ones with Grignard reagents to produce bridged benzo[b]oxocin-2-ols is reported. Mechanistic studies indicate that an iron redox catalysis cycle involving oxidative addition to the C-O bond by low-valence iron and β-methoxyl elimination as key steps operates in this reaction.

Exploring the Divergent Reactivity of Vinyl Radicals Emanating from Alkynes and Thiols via Photoredox Catalysis

Organic chemistry has seen a surge in visible-light-driven transformations, which offer unique reaction pathways and access to new synthetic possibilities. We aim to provide a comprehensive understanding of state-of-the-art photo-mediated alkyne functionalization, with a focus on the reactive behavior of vinyl radicals. This review outlines our contributions to the field, including developing new methods for forming carbon-carbon and carbon-heteroatom bonds.

Chemodivergent Synthesis of Indeno[1,2-b]indoles and Isoindolo[2,1-a]indoles via Mn(III)-Mediated or Electrochemical Intramolecular Radical Cross-Dehydrogenative Coupling

Chemodivergent synthesis of indeno[1,2-b]indoles and isoindolo[2,1-a]indoles from the same starting materials involving radical cross-dehydrogenative couplings have been developed. Mn(OAc)₃·2H₂O selectively promoted an intramolecular radical C-H/C-H dehydrogenative coupling reaction to provide indeno[1,2-b]indoles, while an intramolecular radical C-H/N-H dehydrogenative coupling reaction could proceed via electrochemistry to deliver isoindolo[2,1-a]indoles. Plausible mechanisms of the chemodivergent reactions were proposed.

The solvent-controlled Rh(III)-catalyzed switchable [4+2] annulation of 2-arylIndoles with iodonium ylides

Highly selective and switchable [4+2] annulations of 2-arylindoles with iodonium ylides were achieved by performing solvent-controlled Rh(III)-catalyzed C-H activations. When using DCM as a solvent, the C-H functionalization of 2-arylindoles with iodonium ylides selectively delivered indolo[2,1-a]isoquinoline derivatives. In contrast, the same catalytic system with a polar HFIP solvent predominately provided benzo[a]carbazole moieties.

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.

Rhodium-Catalyzed Annulation of Phenacyl Ammonium Salts with Propargylic Alcohols via a Sequential Dual C-H and a C-C Bond Activation: Modular Entry to Diverse Isochromenones

Given their omnipresence in natural products and pharmaceuticals, isochromenone congeners are one of the most privileged scaffolds to synthetic chemists. Disclosed herein is a dual (ortho/meta) C-H and C-C activation of phenacyl ammonium salts (acylammonium as traceless directing group) toward annulation with propargylic alcohols to accomplish rapid access for novel isochromenones by means of rhodium catalysis from readily available starting materials. This operationally simple protocol features broad substrate scope and wide functional group tolerance. Importantly, the protocol circumvents the need of any stoichiometric metal oxidants and proceeds under aerobic conditions.

Synthesis of Indolo[2,1-a]benzazepinones through Rhodium-Catalyzed Cascade Reactions of 2-Arylindoles with Allyl Alcohols

An efficient synthesis of indolo[2,1-a]benzazepinones through rhodium-catalyzed cascade reactions of 2-arylindoles with allyl alcohols has been developed. This work expands the scope of products that are available through C-H activation/intramolecular annulation reactions of 2-arylindoles in organic synthesis.

Rh(iii)-catalyzed regioselective C-H activation dialkenylation/annulation cascade for rapid access to 6H-isoindolo[2,1-a]indole

6H-isoindolo[2,1-a]indoles were accessed via a Rh(iii)-catalyzed N-H free indole directed C-H activation dialkenylation/annulation cascade in moderate to excellent yields. This protocol also features: reaction procedures that are insensitive to air and moisture, excellent regioselectivity and good functional group tolerance.

In(ONf)3-catalyzed 7-membered carbon-ring-forming annulation of heteroarylindoles with α,β-unsaturated carbonyl compounds

We developed the two recipes, on the indium-catalyzed reductive and oxidative 7-membered carbon-ring-forming annulations of heteroarylindoles with a,β-unsaturated carbonyl compounds.

Dual C–H activation: Rh(iii)-catalyzed cascade π-extended annulation of 2-arylindole with benzoquinone

A rhodium-catalyzed, N–H free indole directed cyclization reaction of benzoquinone via a dual C–H activation strategy is disclosed. This protocol has a good functional group tolerance and affords useful indole-fused heterocylces. Besides, it is insensitive to moisture, commercially available solvent can be directly used and work quite well for this transformation.

A Rh-catalyzed cascade annulation of N–H free 2-arylindole with benzoquinone via dual C–H activation strategy was reported.