Facile access to 2,2-diaryl 2H-chromenes through a palladium-catalyzed cascade reaction of ortho-vinyl bromobenzenes with N-tosylhydrazones

Synthesis of substituted 2H-Chromenes via Pd-catalyzed C-H activation and thermal cyclization

A proficient approach has been developed for the synthesis of substituted 2H-chromenes from C1-substituted glucal. The key step of our synthetic methodology was C-H activation in propylene carbonate solvent followed by 6π-electrocyclization aromatization in ethylene glycol as greener substitutes to toxic aprotic solvents, to obtain 2H-chromenes in a stepwise manner. The application of the developed methodology was further explored with the synthesis of a small library of substituted 2H-chromenes in good yields.

Tunable Construction of Multisubstituted 1,3-Dienes and Allenes via a 1,4-Palladium Migration/Carbene Insertion Cascade

Efficient palladium-catalyzed vinylic C-H alkenylation and allenylation of gem-disubstituted ethylenes with N-tosylhydrazones of aryl alkyl and diaryl ketones were achieved to access trisubstituted 1,3-dienes and tetrasubstituted allenes, respectively. An aryl to vinyl 1,4-palladium migration/carbene insertion/β-hydride elimination sequence proceeded to switch the chemo- and regioselectivities to give structurally diverse products. Use of 2-FC₆H₄OH additive enables enhancement of the reaction efficiency through accelerating the key 1,4-palladium migration process.

Copper(II)-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes to 2,2-disubstituted 2-alkynylated 2H-chromenes

The first copper-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes has been uncovered. The use of cheap and readily available CuCl₂ as the catalyst allowed the preparation of various 2,2-disubstituted 2-alkynylated 2H-chromenes in moderate to good yields, which compensates for the limitation of the current methods only suited for the synthesis of 2-monosubsituted 2-alkynylated 2H-chromenes.

Palladium-Catalyzed Sequential C-H Activation/Amination with Diaziridinone: An Approach to Indoles

Indoles are an important class of molecules. This paper describes an efficient palladium-catalyzed synthesis of indoles from 2-iodostyrenes and di-t-butyldiaziridinone with a simultaneous installation of two C-N bonds. The reaction process likely proceeds through the oxidative insertion of Pd to aryl iodide and subsequent vinyl C-H activation to from a pallada(II)cycle intermediate, which is bisaminated by di-t-butyldiaziridinone to give the indole product.

A 1,4‐Palladium Migration/Heck Sequence with Unactivated Alkenes: Stereoselective Synthesis of Trisubstituted 1,3‐Dienes

The palladium‐catalyzed cross‐coupling of ortho‐vinyl aromatic bromides and olefins was achieved through a controllable 1,4‐palladium migration/Heck cascade protocol. The reaction represents a mild, efficient and highly stereoselective method for the synthesis of trisubstituted 1,3‐dienes, especially for triaryl‐substituted ones.

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Divergent synthesis of 1,3,5-tri and 1,3-disubstituted pyrazoles under transition metal-free conditions

Pyrazole cores are common structural motifs existing in various agrochemicals and pharmaceuticals. Herein, a transition metal-free, three-component reaction of arylaldehydes, ethyl acrylate and N-tosylhydrazones is described, which leads to the formation of 1,3,5-trisubstituted and 1,3-disubstituted pyrazoles divergently under slightly different conditions.

Stereoselective synthesis of conjugated trienes via 1,4-palladium migration/Heck sequence

An efficient 1,4-palladium migration/Heck sequence was developed for the highly stereoselective synthesis of conjugated trienes.