One-Pot Synthesis of Highly Substituted Polyheteroaromatic Compounds by Rhodium(III)-Catalyzed Multiple CH Activation and Annulation

An Orchestrated Unsymmetrical Annulation Episode of C(sp2)-H Bonds with Alkynes and Quinones: Access to Spiro-isoquinolones

A nontrivial Ru-catalyzed one-pot sequential oxidative coupling of a (hetero)arene/vinylic/chromene system with alkyne and quinone is presented; the methyl phenyl sulfoximine (MPS) directing group is vital. This cyclization forms four (two C-C and two C-N) bonds in a single operation and produces unusual spiro-fused-isoquinolones with a broad scope. The release of phenyl methyl sulfoxide makes the MPS group transformable. A deuterium scrambling study sheds light on the reaction path.

Rhodium-catalyzed C-C coupling reactions via double C-H activation

Various rhodium-catalyzed double C-H activations are reviewed. These powerful strategies have been developed to construct C-C bonds, which might be widely embedded in complex aza-fused heterocycles, polycyclic skeletons and heterocyclic scaffolds. In particular, rhodium(iii) catalysis shows good selectivity and reactivity to functionalize the C-H bond, generating reactive organometallic intermediates in most of the coupling reactions. Generally, intermolecular, intramolecular and multi-component coupling reactions via double C-H activations with or without heteroatom-assisted chelation are discussed in this review.

Copper-catalyzed cyclization of 2-cyanobenzaldehydes and 2-isocyanoacetates: an efficient strategy for the synthesis of substituted 1-aminoisoquinolines

An efficient strategy for the synthesis of substituted 1-aminoisoquinoline has been developed.

Synthesis of Phenalenyl-Fused Pyrylium Cations: Divergent C-H Activation/Annulation Reaction Sequence of Naphthalene Aldehydes with Alkynes

Described herein is the synthesis of stable oxonium-doped polycyclic aromatic hydrocarbons (PAHs) by the rhodium-catalyzed C-H activation/annulations of naphthalene-type aldehydes with internal alkynes. This protocol provides four divergent reaction types, including two unexpected annulations with an oxygen transposition process, which lead to diverse types of phenalenyl-fused pyrylium cations comprising a four-, five-, or six-ring-fused π-conjugated core. The annulations exhibit an exquisite regioselectivity and a high tolerance of sensitive functional groups. These PAHs feature intriguing photophysical properties such as full-color tunable fluorescence emission, high quantum yield, and positively charged core, and can be reduced easily to the phenalenyl radicals.

C-H Activation and Alkyne Annulation via Automatic or Intrinsic Directing Groups: Towards High Step Economy

Direct transformation of carbon-hydrogen bond (C-H) has emerged to be a trend for construction of molecules from building blocks with no or less prefunctionalization, leading high atom and step economy. Directing group (DG) strategy is widely used to achieve higher reactivity and selectivity, but additional steps are usually needed for installation and/or cleavage of DGs, limiting step economy of the overall transformation. To meet this challenge, we proposed a concept of automatic DG (DG^auto ), which is auto-installed and/or auto-cleavable. Multifunctional oxime and hydrazone DG^auto were designed for C-H activation and alkyne annulation to furnish diverse nitrogen-containing heterocycles. Imidazole was employed as an intrinsic DG (DGⁱⁿ ) to synthesize ring-fused and π-extended functional molecules. The alkyne group in the substrates can also be served as DGⁱⁿ for ortho-C-H activation to afford carbocycles. In this account, we intend to give a review of our progress in this area and brief introduction of other related advances on C-H functionalization using DG^auto or DGⁱⁿ strategies.

Unified synthesis of mono/bis-arylated phenols via RhIII-catalyzed dehydrogenative coupling

2,6-Bis-arylated phenols are rarely reported and are synthetically challenging. Directed C-H functionalization reactions, using a directing group (DG), might provide a convenient solution to their synthesis. However, this strategy usually results in partial cleavage of the directing group, preventing further/second C-H activation cascades. Herein we report a general strategy that allows for the precise control of the oxidation pathways so that directing groups can be either preserved or cleaved. We found that N-phenoxyacetamides could undergo ortho-arylation reactions with or without an external oxidant, yielding products with different oxidation states, notably the rare bis-arylated phenols. Notably, a unique rhodacycle intermediate was isolated, characterized by X-ray crystallography, and confirmed to be an active catalyst. Switching between internal and external oxidation could be a general strategy in diverse directed C-H functionalization reactions to realize bis-functionalized products.

Expeditious synthesis of pyrano[2,3,4-de]quinolines via Rh(iii)-catalyzed cascade C–H activation/annulation/lactonization of quinolin-4-ol with alkynes

One-step synthesis of tetracyclic pyrano[2,3,4-de]quinolones via Rh(iii)-catalyzed cascade C–H activation/annulation/lactonization is described.

Facile one-pot synthesis of 2,3-dihydro-1H-indolizinium derivatives by rhodium(iii)-catalyzed intramolecular oxidative annulation via C–H activation: application to ficuseptine synthesis

Various substituted indolizidinium, quinolizinium and pyrido[1,2-a]azepinium salts were synthesized from benzaldehydes (α,β-unsaturated aldehydes) and alkyne–amines via Rh-catalyzed C–H activation.

Ru(ii)-Catalyzed annulation of benzamidines and alkynes by C–H/N–H activation: a facile synthesis of 1-aminoisoquinolines

Ru(ii)-Catalyzed annulation reaction of benzamidines and disubstituted alkynes affords 1-aminoisoquinolines.

Ru-Catalyzed One-Pot Diannulation of Heteroaryls: Direct Access to π-Conjugated Polycyclic Amides

A novel Ru-catalyzed oxidative double annulation of heteroarenes with symmetrical and unsymmetrical alkynes is reported. A general method for the unsymmetrical annulation of heteroarenes with two distinct alkynes is showcased for the first time. Methylphenyl sulfoximine (MPS) plays an important role in the annulations of heteroarenes and allows the construction of structurally complex π-conjugated heteroarene-fused polycyclic amide skeletons via the formation of multiple C-C and C-N bonds in a single operation. The reaction exhibits excellent substrate scope and tolerates a wide range of functional groups.

One-Pot Synthesis of Decahydropyrene via Tandem C-H Activation/Intramolecular Diels-Alder/1,3-Dipolar Cycloaddition

A novel decahydropyrene synthesis has been successfully developed involving a tandem rhodium-catalyzed C-H activation/intramolecular Diels-Alder reaction/1,3-dipolar cycloaddition cascade process by using diazole as a traceless directing group. The advantage of this one-pot strategy is a quite simple, efficient, highly stereoselective, and unique product structure.

Synthesis of Natural Product-like Polyheterocycles via One-Pot Cascade Oximation, C-H Activation, and Alkyne Annulation

An efficient protocol for the direct transformation of chroman-4-ones to tricyclic fused pyridines with the skeleton of cassiarins, a family of alkaloids with antimalarial activity, was developed. Also, a general strategy for modular construction of polyheterocycles with diverse natural product-like skeletons was developed by using ketone-alkyne bifunctional substrates. These reactions involved a one-pot cascade oximation of ketones, rhodium-catalyzed C-H activation, and intermolecular/intramolecular alkyne annulations under mild conditions with high atom, step, and redox economy.

Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.