Copper-Catalyzed N-Allenylation of Allylic Sulfonamides

γ-CF3-Allenamides versus 3-CF3-Cyclopentenylamines: Substituent-Controlled Divergent Reaction of β-CF3-1,3-Enynamides with β-Dicarbonyl Compounds

A distinctive N-substituent-controlled regioselective 1,4-hydrocarbonation or 1,4-hydrocarbonation/5-endo-trig cyclization cascade reaction of β-CF3-1,3-enynamides with β-dicarbonyl compounds in the presence of a simple base is reported. β-CF3-1,3-enynamides having a Ts group N-substituent produce γ-CF3-allenamides via a 1,4-hydrocarbonation process, whereas β-CF3-1,3-enynamides bearing a Ms group N-substituent lead to 3-CF3-cyclopentenylamines through a 1,4-hydrocarbonation/5-endo-trig cyclization cascade process.

Cu-Catalyzed Regioselective Silylation of Chloro-Substituted Allenyl-Bdan

A copper-catalyzed efficient regioselective silylation reaction of chloro-substituted allenyl-Bdan was developed. Under mild reaction conditions, allenyl and propargyl silane compounds can be selectively obtained in moderate to high yields by adjusting the bases and solvents used in the reactions. This study offers direct and efficient methods for synthesizing multifunctionalized allenyl and propargyl silane compounds from the same initial material of chloro-substituted allenyl-Bdan.

One-Pot anti-Michael Regio- and Stereoselective Hydroamination of Activated N-Allenamides

N-Allenamides, substituted by an ester at the γ-position, were obtained through addition of terminal ynamides with ethyl diazoacetate under copper catalysis for the first time. Regio- and stereoselective hydroamination of those activated N-allenamides provided exclusively E-configured captodative enamimes through a one-pot anti-Michael addition. Numerous ynamides as well as various secondary amines were adapted in this process.

Copper-catalyzed radical approach to allenyl iodides

A copper-catalyzed 1,4-addition reaction of arylsulfonyl iodides with 1,3-enynes afforded various allenyl halides in high yields under mild conditions via a radical mechanism.

Synthesis of 3-Substituted 3-Bromo-1-phenylallenes from Alkynylcycloheptatrienes

A new method has been developed for the preparation of 3-bromo-1-phenylallenes from 7-alkynylcycloheptatrienes and N-bromosuccinimide. Trisubstituted bromoallenes were obtained at room temperature in moderate to excellent yields. Functionalization of the carbon-bromine bond via Pd- or Cu-catalyzed cross-coupling reactions easily provided substituted allenes.

Designed Bifunctional Phosphine Ligand-Enabled Gold-Catalyzed Isomerizations of Ynamides and Allenamides: Stereoselective and Regioselective Formation of 1-Amido-1,3-dienes

By using designed biphenyl-2-ylphosphines functionalized with a remote basic groups as ligands, N-alkynyl-o-nosylamides are directly converted to (1E,3E)-1-amido-1,3-dienes with excellent diastereoselectivities under gold catalysis. With allenamides as substrates, the gold-catalyzed isomerizations are high yielding and applicable to a broad substrate scope including various nitrogen protecting groups and exhibit unprecedented (3E)-selectivities for the distal C-C double bond and good regioselectivities. Combining this gold catalysis with one-pot Diels-Alder reactions leads to rapid assembly of valuable bicyclic compounds.

Regioselective 1,2-addition of allenamides with N-haloimides: synthesis of 2-halo allylic aminal derivatives

A strategy for the synthesis of 2-halo allylic aminal derivatives through regioselective 1,2-addition of allenamides with N-haloimides is presented. This reaction was conducted under very mild conditions and gave up to 99% yield. Moreover, the obtained halides allow functional group diversification by palladium-catalyzed coupling reactions, which could act as potential intermediates for the synthesis of valuable compounds.

Palladium(II)/Brønsted Acid-Catalyzed Enantioselective Oxidative Carbocyclization-Borylation of Enallenes

An enantioselective oxidative carbocyclization-borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol-type chiral phosphoric acids were superior co-catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess.

Synthesis of functionalized allenamides from ynamides by enolate Claisen rearrangement

The Claisen rearrangement of N-Boc glycinates derived from ynamido-alcohols affords an efficient and stereoselective access to highly functionalized allenamides. These compounds undergo silver-catalyzed cyclization to 3-pyrrolines which are useful precursors for the synthesis of substituted pyrrolidines.

Oppolzer-type intramolecular Diels-Alder cycloadditions via isomerizations of allenamides

A new approach to Oppolzer's intramolecular Diels-Alder cycloaddition (IMDA) through γ-isomerization of readily available N-tethered allenamides is described. These IMDA reactions are carried out in tandem with the allenamide isomerization or 1,3-H shift, leading to complex nitrogen heterocycles in a highly stereoselective manner.

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

Preparations of de novo acyclic 2-amido-dienes and 3-amido-trienes through 1,3-hydrogen shifts from allenamides are described. These 1,3-hydrogen shifts could be achieved thermally or they could be promoted by the use of Brønsted acids. Under either condition, these processes are highly regioselective in favour of the α-position, and highly stereoselective in favour of the E-configuration. In addition, 6π-electron electrocyclic ring-closure could be carried out with 3-amido-trienes to afford cyclic 2-amido-dienes, and such electrocyclic ring-closure could be rendered in tandem with the 1,3-hydrogen shift.

How easy are the syntheses of allenes?

This short review highlights some of the recent important developments on the synthesis of allenes and its applications on the synthesis of some allenic natural products and allenic-based optoelectronic materials.

Stereoselective 6π-electron electrocyclic ring closures of 2-halo-amidotrienes via a remote 1,6-asymmetric induction

A diastereoselective 6π-electrocyclic ring closure employing halogen-substituted 3-amidotrienes via a 1,6-remote asymmetric induction is described. This new asymmetric manifold for pericyclic ring closure further underscores the significance of the allenamide chemistry.

Torquoselective ring closures of chiral amido trienes derived from allenamides. A tandem allene isomerization-pericyclic ring-closure-intramolecular Diels-Alder cycloaddition

A new torquoselective ring-closure of chiral amide-substituted 1,3,5-hexatrienes and its application in tandem with [4 + 2] cycloaddition are described. The trienes were derived via either a 1,3-H or 1,3-H-1,7-H shift of alpha-substituted allenamides, and the entire sequence through the [4 + 2] cycloaddition could be in tandem from allenamides.

Diamine Ligands in Copper-Catalyzed Reactions

The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands has been important in these advances and in this review we discuss these systems, including the choice of reaction conditions and applications in the synthesis of pharmaceuticals, natural products and designed materials.