Copper-Mediated Coupling of 1,1-Dibromo-1-alkenes with Nitrogen Nucleophiles: A General Method for the Synthesis of Ynamides

Cationic polycyclization of ynamides: building up molecular complexity

Polycyclization reactions are among the most efficient synthetic tools for the synthesis of complex, polycyclic molecules in a single operation from simple starting materials. We report in this manuscript a full account on the discovery and development of a novel cationic polycyclization from readily available ynamides. Simple activation of these building blocks under acidic conditions enables the generation of highly reactive activated keteniminium ions, which triggers an unprecedented cationic polycyclization yielding highly substituted polycyclic nitrogen heterocycles possessing up to seven fused cycles and three contiguous stereocenters.

(IPr)CuF-catalyzed α-site regiocontrolled trans-hydrofluorination of ynamides

With Et3N·3HF as the fluorination reagent, (IPr)CuF-catalyzed α-site regiocontrolled trans-hydrofluorination of ynamides has been achieved, affording (Z)-α-fluoroenamides in moderate to excellent yields. It was interesting to note that the regioselectivity of the reaction is reversed to that observed in the (Ph3P)3CuF-catalyzed hydrofluorination of ynamides. Additionally, a variety of different ynamides including oxazolidinonyl-, imidazolyl-, and N-sulfonyl ynamides were suitable for the reaction system and the subsequent oxidation of the fluorinated products enables a convenient synthesis to α-fluoroimides.

NaOH-promoted reaction of 1,1-dihaloalkenes and 1H-azoles: synthesis of dihetaryl substituted alkenes

We have developed a useful and simple process for the NaOH-promoted reaction of 1,1-dihaloalkenes and 1H-azoles to afford dipyrazolyl alkenes under mild and transition-metal-free conditions.

Copper-Catalyzed Alkenylation of Cyanamides

An efficient procedure for the copper-catalyzed cross-coupling between a broad range of cyanamides and iodoalkenes is reported. Upon reaction with catalytic amounts of copper(I) iodide and 2,2'-bisimidazole in the presence of cesium carbonate in DMF at 80 °C, a fast, regioselective, and stereoretentive cross-coupling occurs. This reaction, which was found to have a broad substrate scope, provides the first general entry to N-alkenylcyanamides, building blocks that hold great synthetic potential.

Highly regio- and stereoselective trans-iodofluorination of ynamides enabling the synthesis of (E)-α-fluoro-β-iodoenamides

A highly regio- and stereoselective trans-iodofluorination reaction of ynamides with NIS and Et₃N·3HF has been achieved, affording (E)-α-fluoro-β-iodoenamides in moderate to good yields. The reaction proceeds under mild reaction conditions and exhibits good functional group compatibility.

Copper-catalyzed direct alkylation of heteroarenes

An efficient and broadly applicable process is reported for the direct alkylation of C-H bonds in heteroarenes, privileged scaffolds in many areas of science. This reaction is based on the copper-catalyzed addition of alkyl radicals generated from activated secondary and tertiary alkyl bromides to a wide range of arenes, including furans, thiophenes, pyrroles, and their benzo-fused derivatives, as well as coumarins and quinolinones.

Harnessing the Electrophilicity of Keteniminium Ions: A Simple and Straightforward Entry to Tetrahydropyridines and Piperidines from Ynamides

An efficient, modular and straightforward entry to tetrahydropyridines and piperidines is reported. This reaction is based on a formal intramolecular hydroalkylation of readily available, properly substituted ynamides which, upon simple activation under acidic conditions, generate highly reactive activated keteniminium ions whose reactivity can be finely controlled to induce a remarkably efficient [1,5]-hydride shift from unactivated C-H bonds and trigger a cationic cyclization which is complete within minutes.

Divergent C-H Insertion-Cyclization Cascades of N-Allyl Ynamides

Gold carbene reactivity patterns were accessed by ynamide insertion into a C(sp(3) )H bond. A substantial increase in molecular complexity occurred through the cascade polycyclization of N-allyl ynamides to form fused nitrogen-heterocycle scaffolds. Exquisite selectivity was observed despite several competing pathways in an efficient gold-catalyzed synthesis of densely functionalized C(sp(3) )-rich polycycles and a copper-catalyzed synthesis of fused pyridine derivatives. The respective gold-keteniminium and ketenimine activation pathways have been explored through a structure-reactivity study, and isotopic labeling identified turnover-limiting CH bond-cleavage in both processes.

Ynamide carbopalladation: a flexible route to mono-, bi- and tricyclic azacycles

Bromoenynamides represent precursors to a diversity of azacycles by a cascade sequence of carbopalladation followed by cross-coupling/electrocyclization, or reduction processes. Full details of our investigations into intramolecular ynamide carbopalladation are disclosed, which include the first examples of carbopalladation/cross-coupling reactions using potassium organotrifluoroborate salts; and an understanding of factors influencing the success of these processes, including ring size, and the nature of the coupling partner. Additional mechanistic observations are reported, such as the isolation of triene intermediates for electrocyclization. A variety of hetero-Diels-Alder reactions using the product heterocycles are also described, which provide insight into Diels-Alder regioselectivity.

Stereoselective Synthesis of (2Z)-2,4-Dienamides via NBS-Mediated Allyloxyl Addition-Claisen Rearrangement-Dehydrobromination Cascade Reaction of Ynsulfonamides

An NBS-promoted allyloxyl addition-Claisen rearrangement-dehydrobromination cascade reaction has been developed. More than 20 substituted alkynylsulfonamides were reacted with allyl alcohols to generate (2Z)-2,4-dienamides in moderate to high yields. A mechanistic model has been proposed to account for the overall reaction sequence including the stereochemical outcome. Theoretical calculations suggested that a [3,3] sigmatropic rearrangement be the rate-limiting step.

Cu-catalyzed aerobic oxidative three-component coupling route to N-sulfonyl amidines via an ynamine intermediate

Cu-catalyzed aerobic oxidative three-component coupling of a terminal alkyne, secondary amine, and sulfonamide enables efficient synthesis of amidines. The use of Cu(OTf)2 (5 mol %) produces amidines selectively without Glaser-Hay alkyne homocoupling products. Preliminary studies suggest that the reaction pathway involves initial oxidative coupling of the terminal alkyne with the secondary amine, followed by hydroamidation of the ynamine intermediate with the sulfonamide.

Chemo- and stereoselective synthesis of fluorinated enamides from ynamides in HF/pyridine: second-generation approach to potent ureas bioisosteres

(E)- and (Z)-α-fluoroenamides could be easily prepared with high levels of chemo- and regioselectivities by hydrofluorination of readily available ynamides with HF/pyridine. The scope and limitations of this new process for the hydrofluorination of ynamides, as well as the stability of the resulting α-fluoroenamides, have been extensively studied. Theoretical calculations at the MP2 and B3LYP levels of theory showed that the resulting fluoroenamides exhibit geometrical and electronic properties that partially mirror those of ureas, therefore demonstrating that the hydrofluorination of ynamides provides a general, straightforward, and user-friendly approach to bioisosteres of ureas, potent building blocks for biological studies and medicinal chemistry.

De novo synthesis of functionalized 1,3-enynes and extended conjugated molecular systems

Pd-catalyzed coupling of 1,3-dienyldibromides with triarylbismuths was demonstrated for the synthesis of a diverse range of 1,3-enynes.

A robust and modular synthesis of ynamides

A flexible, modular ynamide synthesis is reported that uses a wide range of amides and electrophiles, including acyclic carbamates, hindered sulfonamides, and aryl amides.

1,2-N-migration in a gold-catalysed synthesis of functionalised indenes by the 1,1-carboalkoxylation of ynamides

Unique α-hemiaminal ether gold carbene intermediates were accessed by a gold-catalysed 1,1-carboalkoxylation strategy and evolved through a highly selective 1,2-N-migration. This skeletal rearrangement gave functionalised indenes, and isotopic labelling confirmed the rare C–N bond cleavage of the ynamide moiety. The effect of substituents on the migration has been explored, and a model is proposed to rationalise the observed selectivity.

Syntheses of indolizinones from an intramolecular one-pot process of gem-dibromoolefins

A rare type of indolizinone is constructed from an Intramolecular one-pot process from gem-dibromoolefins.

Turning unreactive copper acetylides into remarkably powerful and mild alkyne transfer reagents by oxidative umpolung

Upon oxidation, copper acetylides formally behave as highly electrophilic species that could be trapped by a wide range of nucleophiles.

A gold-catalysed fully intermolecular oxidation and sulfur-ylide formation sequence on ynamides

A chemoselective three-component oxidation-intermolecular sulfur ylide formation-rearrangement sequence provides efficient access to functionalised tertiary thioethers from ynamides.

Benzannulation via the reaction of ynamides and vinylketenes. application to the synthesis of highly substituted indoles

A two-stage "tandem strategy" for the synthesis of indoles with a high level of substitution on the six-membered ring is described. Benzannulation based on the reaction of cyclobutenones with ynamides proceeds via a cascade of four pericyclic reactions to produce multiply substituted aniline derivatives in which the position ortho to the nitrogen can bear a wide range of functionalized substituents. In the second stage of the tandem strategy, highly substituted indoles are generated via acid-, base-, and palladium-catalyzed cyclization and annulation processes.

Copper-Catalysed Regio- and Stereoselective Addition of n-Heterocycles to gem-Dihalo-Olefins: Synthesis of Useful N-Vinyl Halides

A facile synthesis of N-vinyl halides via a Cu(I)-catalysed highly regio- and stereoselective addition of imidazoles or benzimidazoles to gem-dihalo-olefins was reported. The reaction proceeded smoothly in the presence of TBAB to afford the desired products in moderate to good yields. Application to the synthesis of aryl vinyl ethers derivatives is demonstrated.