Facile access to C-substituted piperazin-2-ones and mianserin derivative enabled by chemoselective carbene insertion and cyclization cascade.

The chemoselective N-H insertion of unsymmetrical diamines into carbene is a longstanding challenge. A simple copper-catalyzed strategy for synthesizing C-substituted piperazinones is described, employing easily accessible diazo compounds and 1,2-diamines. The reaction proceeded via chemo-selective carbene insertion at the comparatively less nucleophilic amine, followed by instantaneous cyclization. The protocol was further extended to access NH-free piperazinone, and the synthesis of a Mianserin derivative.

Regio- and Stereoselective Hexafluoroisopropoxylation and Trifluoroethoxylation of Allenamides.

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio- and stereoselective manner in good to moderate yields under mild conditions.

Metal-free transfer hydrogenation/cycloaddition cascade of activated quinolines and isoquinolines with tosyl azides.

The difficulty in isolating cyclic enamines emanating from their intrinsic instability has impeded their exploration in cycloaddition reactions. Here, we achieved a metal-free domino reaction providing quinoline and isoquinoline-derived cyclic amidines by the cycloaddition of azides with in situ generated enamines via dearomatization.

Palladium-Catalyzed C(sp3)-H Biarylation of 8-Methyl Quinolines with Cyclic Diaryliodonium Salts to Access Functionalized Biaryls and Fluorene Derivatives.

Herein, we have developed the cyclic diaryliodonium salts as biarylating agents in the C(sp3)-H functionalization using 8-methyl quinoline as the intrinsic directing group. The oxidant-free reaction produces a vast array of the biarylated products with iodo functionality that can be further functionalized. Additionally, intramolecular C(sp3)-H functionalization in a stepwise manner under palladium-catalyzed conditions produced the fluorene derivatives in excellent yields.

Copper-catalyzed cascade reaction of tryptamines with diazo compounds to access hexahydropyrroloindoline derivatives.

A domino reaction sequence of cyclopropanation/ring-opening/iminium cyclization of tryptamine derivatives with donor-acceptor diazo compounds is developed to furnish pyrroloindolines, creating three consecutive stereogenic centers in a single step. The copper-catalyzed reaction provides pyrroloindolines at room-temperature with good substrate scope.

Regiodivergent cascade cyclization/alkoxylation of allenamides via N-protecting group driven rearrangement to access indole and indoline derivatives.

A mild, palladium-catalyzed domino Heck-cyclization/alkoxylation sequence of aryl halide tethered allenamides is described, providing regiodivergent indole and indoline derivatives controlled by the N-protecting group. This room temperature reaction provided a functionalizable olefinic moiety with broad substrate scope. Preliminary mechanistic studies support the rearrangement of an indoline-derived intermediate to indoles with the N-acetyl allenamides forming free (NH) indoles.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles.

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a renewable hydrogen source and an Ir catalyst for the reduction of quinolines and pyridines. The reaction is promoted by simple amides as ligands.

Dicarbofunctionalization of unactivated alkenes by palladium-catalyzed domino Heck/intermolecular direct hetero arylation with heteroarenes.

A palladium-catalyzed domino Heck/intermolecular direct hetero arylation sequence of unactivated alkenes was developed, providing 1,2,3-triazole containing bisheterocycles bearing all-carbon quaternary centers with yields of 25-90%. The protocol was extended to 1,3,4-oxadiazoles as well. The installed triazole was further exploited for late-stage functionalizations, and the mechanistic studies indicate the involvement of C-H activation.

A palladium and gold catalytic system enables direct access to O- and S-linked non-natural glyco-conjugates.

Here we report a straightforward cross-coupling method for the synthesis of non-natural glycoamino acids from alkyne-bearing monosaccharides and p-iodophenylalanine. Pd/Au-catalyzed Sonogashira coupling is tolerant to both O- and S-glycosides without any epimerization. In addition, no racemization of the amino acid was observed allowing direct access to the homogeneous glyco-conjugate in a single step. Notably, this Pd/Au catalytic system presents enhanced catalytic activity than conventional Pd/Cu and Pd-only platforms, and it further enables the convergent synthesis of glycodipeptides.

Silver(I)-catalyzed reaction between pyrazole and propargyl acetates: stereoselective synthesis of the scorpionate ligands (E)-allyl-gem-dipyrazoles (ADPs).

The reaction between readily accessible pyrazole and propargyl acetates in the presence of Ag(I) catalyst yielded a new class of (E)-allyl-gem-dipyrazole scorpionate ligands: 1-aryl-2-N-pyrazolyl allyl acetates and 1,3-dipyrazolyl-3-arylpropene. The reaction showed broad substrate scope, and various functional and protecting groups were tolerated under the reaction conditions. The palladium(II) scorpionate complex could thus be easily prepared and successfully employed in Suzuki-Miyaura cross-couplings in water.

Direct access to benzo[b]furans through palladium-catalyzed oxidative annulation of phenols and unactivated internal alkynes.

2,3-Disubstituted benzo[b]furans are prepared in one step from commercially available phenols and readily accessible unactivated internal alkynes (see scheme). This Pd-catalyzed oxidative annulation has a broad substrate scope and allows access to a wide range of benzo[b]furans.

A convenient approach to ß-heteroarylated (C-N bond) ketones from Cs2CO3 promoted reaction between propargyl alcohols and nitrogen-heterocycles.

An efficient and direct approach to ß-heteroarylated (C-N bond) ketones is demonstrated. Base promoted redox isomerization of propargyl alcohol to α,ß-unsaturated ketone followed by conjugate addition to NH-heteroarenes affords a wide range of ß-heteroarylated ketones in good to excellent yields. Aryl, heteroaryl, alkyl C(sp), and terminal alkynes containing unactivated propargyl alcohols effectively undergo redox-isomerization conjugate addition (RICA) with NH-heteroarenes. Reaction of 3-substituted pyrazoles or indazole with propargyl alcohols enables highly regioselective products. A diverse range of NH-bearing nucleophiles such as: pyrazoles, imidazole, triazoles, pyrrole, indoles and aniline participate in this reaction and deliver the corresponding ß-heteroarylated ketones.

Gold-catalyzed intermolecular hydrophenoxylation of unactivated internal alkynes.

A general and simple strategy for the synthesis of functionally diverse arylvinyl ethers is reported through gold-catalyzed intermolecular addition of electronically and sterically substituted phenols with unactivated alkynes. Addition of phenols to unsymmetrical alkynes provides the corresponding mixture of regioisomers with appreciable selectivity. Multiple hydrophenoxylations of polyphenols with diphenylacetylene are demonstrated successfully.