Rhodium-Catalyzed Borylative Cyclization of 2-Alkynylaryl Isocyanates with Bis(pinacolato)diboron

Synthesis of Bis-Heterocycles Bearing Methyleneindole Motifs by Pd-Catalyzed Domino Reaction

A highly robust, general, and practically simple palladium-catalyzed domino bicyclization strategy is presented to synthesize nitrogen-containing bis-heterocycles bearing methylene indole motifs from alkyne-tethered carbamoyl chlorides and β,γ- or γ,δ-unsaturated hydrazones. The salient features of this transformation include broad substrate scope, good functional group tolerance, ease for scale-up, and convenient conversion.

Binaphthyl-Stabilized Palladium Nanoparticle-Catalyzed Stereoselective Synthesis of 3-Arylidene-2-oxindoles via One-Pot Heck-like Carbocyclization/Nucleophilic Addition

Stereoselective, one-pot synthesis of 3-arylidene-2-oxindoles has been accomplished via Heck-like carbocyclization/nucleophilic addition of N-(2-iodophenyl)-N-methyl-3-phenylpropiolamide, phenylacetylene, and secondary amine using binaphthyl stabilized palladium nanoparticles (Pd-BNP) as a reusable catalyst. Less reactive aryl bromides generally provided a similar yield of 3-arylidene-2-oxindoles compared with more reactive aryl iodides. The Pd-BNP nanocatalyst has been recovered and recycled for five catalytic cycles with only an insignificant reduction in particle size, reactivity, and reaction yield.

Cycloisomerization of Carbamoyl Chlorides in Hexafluoroisopropanol: Stereoselective Synthesis of Chlorinated Methylene Oxindoles and Quinolinones

Hexafluoroisopropanol (HFIP) was employed as an additive for the generation of 3-(chloromethylene)oxindoles via the chloroacylation of alkyne-tethered carbamoyl chlorides. This reaction avoids the use of a metal catalyst and accesses products in high yields and stereoselectivities. Additionally, this reaction is scalable and proved amenable to a series of product derivatizations, including the synthesis of nintedanib. The reactivity of alkene-tethered carbamoyl chlorides with hexafluoroisopropanol (HFIP) was harnessed towards the synthesis of 2-quinolinones.

Copper-catalyzed boroacylation of allenes to access tetrasubstituted vinylboronates

A distinct copper-catalyzed boroacylation of allenes with acyl chlorides and bis(pinacolato)diboron is developed. For aromatic acyl chlorides, 1,2-boroacylation of allenes readily takes place, leading to the formation of tetrasubstituted vinylboronates with exclusive (E)-stereoselectivity. In comparison, the employment of alkyl acyl chlorides as electrophiles alters the selectivity to 2,3-boroacylated products. Additionally, the product can easily undergo Suzuki-Miyaura cross-coupling to afford tetrasubstituted alkene with complete retention of the configuration.

Ru-Catalyzed dehydrogenative synthesis of antimalarial arylidene oxindoles

Ru(ii)-NHC catalyzes α-olefination of 2-oxindoles using diaryl methanols in the absence of an acceptor. A wide array of symmetrical and unsymmetrical diaryl methanols undergoes dehydrogenative coupling with 2-oxindole selectively to generate various substituted 3-(diphenylmethylene)indolin-2-one derivatives in good yields and produces environmentally benign by-products, H2 and H2O. This methodology was successfully applied for the synthesis of a bioactive drug i.e. TAS-301. The biological activities of the synthesized 3-(diphenylmethylene)indolin-2-one derivatives were screened against the Plasmodium falciparum parasite and found to exhibit a significant activity with IC50 = 2.24 μM.

Formal nucleophilic borylation and borylative cyclization of organic halides

Recent advances in borylations of organic halides, including both transition-metal-catalyzed and metal-free methods are summarized. Borylative cyclization is also discussed.

Indium triflate catalysed 3-aza-Cope rearrangement of amino acid derived α,β-unsaturated esters to alkylidene oxindoles

The first examples of amino acid derived α,β-unsaturated esters to Z-alkylidene oxindoles via 3-aza-Cope rearrangement using In(OTf)₃ are reported.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

Six-component reactions for the stereoselective synthesis of 3-arylidene-2-oxindoles via sequential one-pot Ugi/Heck carbocyclization/Sonogashira/nucleophilic addition

An efficient palladium-catalyzed protocol for the synthesis of 3-arylidene-2-oxindoles has been developed. In this approach, a sequential one-pot six-component reaction via Ugi/Heck carbocyclization/Sonogashira/nucleophilic addition was used for the synthesis of the desired skeleton.

Palladium-catalyzed C-H functionalization of N-arylpropiolamides with aryliodonium salts: selective synthesis of 3-(1-arylmethylene)oxindoles

A selective and efficient method for the synthesis of 3-(1-arylmethylene)oxindoles by palladium-catalyzed C-H functionalization of anilides with aryliodonium salts has been developed. In the presence of Pd(OAc)2 and Et3N, a variety of anilides underwent the reaction with aryliodonium salts to afford the corresponding 3-(1-arylmethylene)oxindoles in moderate to good yields. It is noteworthy that the reaction can be conducted providing moderate yields even without bases. The mechanism of the reaction was also discussed.