Rhodium-catalyzed three-component C(sp3)/C(sp2)-H activation enabled by a two-fold directing group strategy

Rh-catalyzed three-component C(sp3)/C(sp2)-H activation has been achieved through a two-directing group strategy. This protocol provides a convenient and efficient pathway for the construction of diverse 8-alkyl quinoline derivatives in one-pot. Furthermore, mechanistic studies revealed that the first C-H amidation was significantly faster than the sequential C-H alkylation.

Co(III)-Catalyzed three-component assembling of N-(2-pyrimidyl) indoles with dienes and formaldehyde

A highly regio- and chemoselective three-component assembling of N-pyrimidyl indoles with dienes and formaldehyde in the presence of a Co(III) catalyst was demonstrated. The scope of the reaction was investigated with a variety of indole derivatives to synthesize substituted homoallylic alcohols. Both butadiene and isoprene units were compatible with the reaction. To understand the reaction mechanism, various investigations were carried out, and suggested the plausibility of a reaction mechanism involving C-H bond activation as a key step.

C-H bond activation and sequential addition to two different coupling partners: a versatile approach to molecular complexity

Sequential multicomponent C-H bond addition is a powerful approach for the rapid, modular generation of molecular complexity in a single reaction. In this approach, C-H bonds are typically added across π-bonds or π-bond isosteres, followed by subsequent coupling to another type of functionality, thereby forming two σ-bonds in a single reaction sequence. Many sequential C-H bond addition reactions have been developed to date, including additions across both conjugated and isolated π-systems followed by coupling with reactants such as carbonyl compounds, cyanating reagents, aminating reagents, halogenating reagents, oxygenating reagents, and alkylating reagents. These atom-economical reactions transform ubiquitous C-H bonds under mild conditions to more complex structures with a high level of regiochemical and stereochemical control. Surprising connectivities and diverse mechanisms have been elucidated in the development of these reactions. Given the large number of possible combinations of coupling partners, there are enormous opportunities for the discovery of new sequential C-H bond addition reactions.

Stereoselective Synthesis of Allenyl Alcohols by Cobalt(III)-Catalyzed Sequential C-H Bond Addition to 1,3-Enynes and Aldehydes

An efficient and stereoselective CoIII -catalyzed sequential C-H bond addition to 1,3-enynes and aldehydes is disclosed. This transformation represents the first example of sequential C-H bond additions to 1,3-enynes and a second coupling partner and provides the first example of preparing allenes by C-H bond addition to 1,3-enynes. A wide range of aldehydes, C-H bond substrates and 1,3-enynes with large substituents on the alkynes are effective substrates. The allenyl alcohol products can be further converted to dihydrofurans with high stereoselectivity either in situ or under Ag-mediated cyclization conditions. The allenyl silyl group can also be transferred to the adjacent alcohol by a Brook rearrangement. Moreover, a mechanism for the transformation is proposed supported by X-ray structural characterization of a cobaltacycle intermediate.

Synthesis of α-Branched Amines by Three- and Four-Component C-H Functionalization Employing a Readily Diversifiable Hydrazone Directing Group

Efficient syntheses of α-branched amines by three- and four-component C-H functionalization employing a diversifiable hydrazone directing group have been developed. The hydrazone in the α-branched amine products has been readily converted to multiple desirable functionalities such as a nitrile, a carboxylic acid, alkenes, and heterocycles using diverse heterolytic chemistry and homolytic transition metal- or photoredox-catalyzed processes. This study represents the first example of a four-component C-H functionalization reaction.

Acyl silane directed Cp*Rh(III)-catalysed alkylation/annulation reactions

Studies into the Cp*Rh(iii)-catalysed hydroarylation of alkenes with aryl acyl silanes led to the discovery of a new synthetic strategy to access unique silicon derived indene frameworks. Rather than protodemetalation of the metal enolate formed following insertion of an alkene into the aryl C-H bond, intramolecular aldol condensation of the acyl silane occurred to generate a series of 2-formyl- and 2-acetyl-3-silyl indenes. This represents only the second example of rhodium-catalysed C-H functionalisation employing acyl silanes as weakly coordinating directing groups and the intramolecular aldol condensation strategy was extended to access analogous silicon derived benzofurans.

Use of Strain-Release for the Diastereoselective Construction of Quaternary Carbon Centers

Herein, we describe the formation of quaternary carbon centers with excellent diastereoselectivity via a strain-release protocol. An organometallic species is generated by Cp*Rh(III)-catalyzed C-H activation, which is then coupled with strained bicyclobutanes (BCBs) and a prochiral carbon electrophile in a three-component reaction. This work illustrates a rare example of BCBs in transition metal catalysis and demonstrates their broad potential to access novel reaction pathways. The method developed exhibits ample functional group tolerance, and the products can be further transformed into valuable α-quaternary β-lactones. Preliminary mechanistic investigations suggest a twofold C-C bond cleavage sequence involving σ-bond insertion and an ensuing β-carbon elimination event.

Intermolecular 1,4-Carboamination of Conjugated Dienes Enabled by Cp*RhIII -Catalyzed C-H Activation

A protocol for the three-component 1,4-carboamination of dienes is described. Synthetically versatile Weinreb amides were coupled with 1,3-dienes and readily available dioxazolones as the nitrogen source using [Cp*RhCl₂ ]₂ -catalyzed C-H activation to deliver the 1,4-carboaminated products. This transformation proceeds under mild reaction conditions and affords the products with high levels of regio- and E-selectivity. Mechanistic investigations suggest an intermediate Rh^III -allyl species is trapped by an electrophilic amidation reagent in a redox-neutral fashion.

Synthesis of Homoallylic Alcohols with Acyclic Quaternary Centers through CoIII -Catalyzed Three-Component C-H Bond Addition to Internally Substituted Dienes and Carbonyls

An efficient Co^III -catalyzed three-component strategy to prepare homoallylic alcohols containing acyclic quaternary centers is disclosed. This transformation enables the introduction of two C-C σ bonds through C-H bond activation and sequential addition to internally substituted dienes and a wide range of aldehydes and activated ketones. Isoprene and other internally monosubstituted dienes are effective inputs, with the reaction proceeding with high diastereoselectivity for those substrate combinations that result in more than one stereogenic center. Moreover, the opposite relative stereochemistry can be achieved by employing 1,2-disubstituted dienes. A mechanism for the transformation is proposed based upon the relative stereochemistry of the products and studies with isotopically labeled starting materials.