Cascade Synthesis of 3-Alkylidene Dihydrobenzofuran Derivatives via Rhodium(III)-Catalyzed Redox-Neutral C–H Functionalization/Cyclization

Hydroxy Group-Enabled Regio- and Stereoselective Hydroalkylation of Alkynyl Cyclobutanol via Palladium-Catalyzed C-C Bond Activation of Cyclopropanol: A One-Step Access to Vinyl Cyclobutanols

The regio-/stereoselective synthesis of vinyl cyclobutanols from alkynyl cyclobutanols is demonstrated. Here, selective C-C bond activation of the cyclopropyl alcohol ring has been achieved in the presence of the cyclobutanol ring. The KIE experiments indicated the noninvolvement of the O-H oxidative addition step in the rate-determining step. Further, the applicability of these vinyl cyclobutanols for the synthesis of 1,4-diketones and 1,6-diketone is demonstrated.

Coupling partner-dependent unsymmetrical C–H functionalization of N-phenoxyacetamides leading to sophisticated spirocyclic scaffolds

In this paper, a coupling partner-dependent unsymmetrical C–H functionalization of N-phenoxyacetamides leading to the formation of sophisticated spirocyclic scaffolds is presented.

Synthesis of non-C2 symmetrical NOBIN-type biaryls through a cascade N-arylation and [3,3]-sigmatropic rearrangement from O-arylhydroxylamines and diaryliodonium salts

We developed herein a regioselective construction of non-C₂ symmetrical NOBIN-type biaryls through a cascade N-arylation and [3,3]-sigmatropic rearrangement from O-arylhydroxylamines and diaryliodonium salts under mild conditions. The employment of copper salt could inhibit the further O-arylation of the newly formed biaryl products, otherwise, O-arylated NOBIN-type products were furnished in moderate to good isolated yields. The products of this protocol can be further converted into highly valuable functional molecules and heterocycles.

Rh(III)-Catalyzed Regioselective Annulations of 3-Arylisoxazolones and 3-Aryl-1,4,2-dioxazol-5-ones with Propargyl Alcohols: Access to 4-Arylisoquinolines and 4-Arylisoquinolones

The Rh(III)-catalyzed dual directing group assisted C-H activation/annulation of 3-arylisoxazolones with propargyl alcohols has been developed, which expands the application scope of isoxazolones in organic synthesis. This protocol also worked well with 3-aryl-1,4,2-dioxazol-5-ones to produce synthetically and biologically important 4-arylisoquinolones.

Directing group migration strategy in transition-metal-catalysed direct C-H functionalization

Very recently, directing group (DG) migration has emerged as a practical strategy for transition-metal-catalysed direct C-H activation, resulting in a highly atom-economical process and enabling the reusage of DG. Therefore, great progress has been made in developing multitasking DGs. In this tutorial review, we present the rapid advances of this novel strategy by analyzing and comparing the different types of migratable DGs (including N-O, N-C, N-N or O-C bond cleavage to trigger DG migration). The related mechanisms, as well as synthetic applications, are also mentioned.

Rhodium(III)-Catalyzed Alkenyl C-H Functionalization to Dienes and Allenes

An oxyacetamide-directed Rh(III)-catalyzed Z-type alkenyl C-H functionalization through a rare exo-rhodacyle intermediate is described, forming multisubstituted dienes and allenes. A variety of alkenes and propargylic carbonate coupling partners are suitable for this transformation with high regio- and stereoselectivity. The synthetic utility is demonstrated by the selective late-stage modification of the Z-type natural products as well as the synthesis of the unnatural β-amino acid.

Ru(II)-Catalyzed and acidity-controlled tunable [5+1]/[5+2] annulation for building ring-fused quinazolines and 1,3-benzodiazepines

The Ru(ii)-catalyzed tunable [5+1]/[5+2] annulation of N-benzo[d]imidazole indolines with propargyl carbonates has been realized for the divergent synthesis of ring-fused quinazolines and 1,3-benzodiazepines bearing various functional groups. These transformations represent an efficient and practical strategy in constructing complex heterocycles via diversified C-H functionalization. A distinctive acidity-controlled reaction manner has been clarified to account for the chemoselectivity.

Synthesis of ortho-Phenolic Sulfilimines via an Intermolecular Sulfur Atom Transfer Cascade Reaction

To expand the toolbox for the synthesis of ortho-phenolic sulfilimines, sigmatropic rearrangements were introduced to the field of sulfilimine chemistry. Herein we report a N-H sulfenylation/[2,3]-sigmatropic rearrangement cascade reaction. This mild reaction enables commercially available thiols to serve as the sulfenylation reagent and generates water as the sole byproduct. Moreover, the reaction has a wide substrate scope and can be conducted on a gram scale with excellent reaction efficiency.

Benzofuran: A Key Heterocycle - Ring Closure And Beyond

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The benzofuranyl motif present in compounds exhibits various medicinal properties and non-drug applications. These derivatives are naturally occurring compounds or synthetic materials, which cover a broad spectrum of pharmacological activities like anti-inflammatory, anti-diabetic, anti- depressant, anti-HIV, anti-microbial, anti-proliferative, anti-convulsant, cytotoxic, analgesic, etc. Few of the commercially interesting compounds from this class are, ailanthoidol (anti-inflammatory), amiodarone, dronedarone, celivarone (anti-arrhythmic), bufuralol (muscular airways relaxant), morphine, 5-(2-aminopropyl)benzofuran; 5-APB, 6-(2-aminopropyl)benzofuran; 6-APB (CNS), rifampicin (antibiotic), etc., whereas, some of the non-drug applications are in perfumery industry (bergapten) and as tannin activators in sunscreen preparations (psoralen, 8-methoxypsoralen, and angelicin). Considering these interesting biological activities and commercial utilities, a review on the synthetic aspects of this privileged scaffold was attempted. For the benefit of natural product-based drug discovery, available sources of these derivatives, extraction process and reported biological activities have also been outlined in this review.

Mild and efficient synthesis of trans-3-aryl-2-nitro-2,3-dihydrobenzofurans on water

A protocol to prepare trans-3-aryl-2-nitro-2,3-dihydrobenzofurans has been developed on water. The protocol avoids the use of toxic solvents, tedious work-up procedures, and chromatographic separation.

Rh(III)-Catalyzed C-H Activation/Cycloisomerization of N-Phenoxyacetamides with Enynones for One-Pot Assembly of Furylated 2-Alkenylphenols

An efficient and practical procedure for one-pot assembly of furylated 2-alkenylphenols has been achieved via the Cp*^CyRh-catalyzed regioselective redox-neutral C-H activation/5-exo-dig cyclization cascade using N-phenoxyacetamides and enynones as the viable substrates. The synthetic application of such a protocol has also been demonstrated to highlight the versatility of this transformation.

Rhodium(iii)-catalysed cascade [3 + 2] annulation of N-aryloxyacetamides with 3-(hetero)arylpropiolic acids: synthesis of benzofuran-2(3H)-ones

Herein, a cascade [3 + 2] annulation of N-aryloxyacetamides with 3-(hetero)arylpropiolic acids affording benzofuran-2(3H)-ones via rhodium(iii)-catalyzed redox-neutral C-H functionalization/isomerization/lactonization using an internal oxidative directing group O-NHAc was achieved. This catalytic system provides a regio- and stereoselective approach to synthesize (Z)-3-(amino(aryl)methylene)benzofuran-2(3H)-ones with exclusive Z configuration selectivity, acceptable yields and good functional group tolerance. Preliminary investigations on ultraviolet-visible and fluorescence behaviors reveal that the annulation products may be applied as a promising fluorescent probe for sensing metal cations, especially for cerium (Ce3+).

One-step access to N-enoxyimides by gold-catalysed addition of N-hydroxyimides to terminal alkynes

A gold(i)trifluoroacetate complex promotes direct additions of N-hydroxyimides to a wide variety of terminal alkynes yielding synthetically valuable N-enoxyimides.

Rapid assembly of cyclopentene spiroisoindolinones via a rhodium-catalysed redox-neutral cascade reaction

A rhodium-catalysed redox-neutral cascade reaction starting from benzamides and cyclopropenones for the rapid assembly of cyclopentene spiroisoindolinones has been developed.

Cascade cyclization and acyl migration of propargylic esters with isocyanides: rapid access to substituted furans

A novel rearrangement of ester-activated propargylic acetate with isocyanide has been disclosed. This protocol enables a quick synthesis of polysubstituted furan derivatives.

Transition-Metal-Free Cyclization of Propargylic Alcohols with Aryne: Synthesis of 3-Benzofuranyl-2-oxindole and 3-Spirooxindole Benzofuran Derivatives ⊥

An unprecedented base-mediated cyclization of propargylic alcohols with aryne is reported, providing a novel method for the synthesis of 3-benzofuranyl-2-oxindole and 3-spirooxindole benzofuran scaffolds via a propargyl Claisen rearrangement/cycloaddition pathway. The nature of the substituent on acetylene group of propargylic alcohol influences the outcome of the reaction. The protocol offers a transition-metal-free and operationally simple methodology with broad substrate scope as a ready access to complex oxindole-linked heterocyclic compounds.

Regioselective Synthesis of Bicyclic and Polycyclic Systems by Cycloaddition Reactions of Alkenyl p-Benzoquinones

An efficient [3 + 2]/[4 + 2] or double [4 + 2] cycloaddition strategy has been established for the synthesis of heterocyclic systems under mild conditions. The reaction pathway is governed by the nature of reaction partner. Several dihydrofurocoumarin, furopyranocoumarin, dihydrofuran, dihydrobenzopyran, and dihydrobenzofuran derivatives were obtained as single diastereomers from cyclic or acyclic enol ethers and styrenes. This one-pot transformation constructed C-C and C-O bonds and generated molecular complexity by domino/tandem process to produce the heterocyclic systems in good yields. The ring closure of domino protocol was highly stereoselective and resulted in the formation of cis-fused systems.

Collective Syntheses of 2-(3-Methylbenzofuran-2-yl)phenol-Derived Natural Products by a Cascade [3,3]-Sigmatropic Rearrangement/Aromatization Strategy

A cascade [3,3]-sigmatropic rearrangement/aromatization strategy to the synthesis of 2-(3-methylbenzofuran-2-yl)phenol derivatives was developed and applied to the collective syntheses of seven 2-arylbenzofuran-containing natural products, namely glycybenzofuran, glycyuralin E, lespedezol A₁, puerariafuran, 7,2',4'-trihydroxy-3-benzofurancarboxylic acid, coumestrol, and 4'-O-methylcoumestrol. Among them, the total syntheses of glycybenzofuran, glycyuralin E, puerariafuran, 7,2',4'-trihydroxy-3-benzofurancarboxylic acid, and 4'-O-methylcoumestrol were reported for the first time. The practicality of this novel strategy in preparation of the key intermediates was demonstrated by performing the reaction on gram scale and by synthesizing a series of natural products with 2-(3-methylbenzofuran-2-yl)phenol scaffolds in a common strategy.

Manganese(I)-Catalyzed Regio- and Stereoselective 1,2-Diheteroarylation of Allenes: Combination of C-H Activation and Smiles Rearrangement

Heteroarenes are important structural motif in functional molecules. A Mn^I -catalyzed 1,2-diheteroarylation of allenes via a C-H activation/Smiles rearrangement cascade is presented. The reaction occurred under additive-free or even solvent-free conditions, which allowed the creation of two C-C and one C-N bonds in a single operation. A series of structurally diverse bicyclic or tricyclic compounds bearing an exocyclic double bond were constructed in good to excellent efficiency. The decarboxylative ring-opening of the products led to the facile synthesis of vicinal biheteroaryls. Synthetic applications were demonstrated and preliminary mechanistic studies were conducted.