Stereoselective Synthesis of Polysubstituted Conjugated Dienes Enabled by Photo-Driven Sequential Sigmatropic Rearrangement

We here reported a highly stereoselective method for the synthesis of polysubstituted conjugated dienes from α-aryl α-diazo alkynyl ketones and pyrazole-substituted unsymmetric aminals under mild conditions, which was promoted by photo-irridation and involved with 1,6-dipolar intermediate and quadruple sigmatropic rearrangements, was successfully developed. In this transformation, the cleavage of four bonds and the recombination of five bonds were implemented in one operational step. This protocol provided a modular tool for constructing dienes from amines, pyrazoles and α-alkynyl-α-diazoketones in one-pot manner. The results of mechanistic investigation indicated that the plausible reaction path underwent the 1,6-sigmatropic rearrangement instead of the 1,5-sigmatropic rearrangement.

Copper-Catalyzed [2 + 2] Cyclization/Ring Expansion of Ene-Ynamides: Construction of Medium- and Large-Sized Rings

Catalytic cyclization of enynes is an efficient approach for the preparation of cyclic compounds, and a large variety of four- to six-membered rings could be synthesized using this method. However, it has been rarely employed for the construction of medium- and large-sized rings. Herein, we describe a copper-catalyzed cycloisomerization of ene-ynamides through a [2 + 2] cyclization/electrocyclic ring opening cascade, leading to the atom-economical assembly of indole-fused medium- and large-sized rings in moderate to excellent yields under mild reaction conditions. Importantly, the synthetic utility of this reaction was demonstrated by the convenient synthesis of iprindole.

Copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations

The enantioselective transformation of easily accessible 1,2-diketones represents a quick pathway towards enantioenriched molecules. Herein, we disclose a copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations, enabling the efficient and atom-economical construction of axially chiral arylpyrroles bearing 1,3-dioxole moieties with good to excellent enantioselectivities under mild reaction conditions. Importantly, this methodology constitutes the first enantioselective formal [4+1] annulation of 1,2-diketones.

Copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles

One-carbon homologation reactions based on one-carbon insertion into the N-O bond of heterocycles have received tremendous interest over the past decades. However, these protocols have to rely on the use of hazardous and not easily accessible diazo compounds as precursors, and examples of the relevant asymmetric catalysis have not been reported. Here we show that a copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles involving one-carbon insertion into the heterocyclic N-O bond via non-diazo approach. This method enables practical and atom-economic synthesis of valuable pyrrole-substituted oxadiazines in generally moderate to good yields under mild reaction conditions. In addition, the possibility of such an asymmetric formal (5 + 1) annulation also emerges.

Catalyst-Free Synthesis of Polycyclic Spiroindolines by Cascade Reaction of 3-(2-Isocyanoethyl)indoles with 1-Sulfonyl-1,2,3-triazoles

A catalyst-free cascade reaction of 3-(2-isocyanoethyl)indoles and 1-sulfonyl-1,2,3-triazoles was realized. This dearomative spirocyclization provided an efficient protocol to synthesize a series of polycyclic indolines bearing spiro-α-carboline in moderate to high yields in one step under thermal reaction conditions.

Construction of Spirolactams by Unexpected Oxidative Cyclization of Alkenyl Diynes via Copper Catalysis

A copper-catalyzed oxidative cyclization of alkenyl N-propargyl ynamides is described. This protocol enables the practical synthesis of diverse spirocyclic γ-lactams bearing an exocyclic double bond with generally high Z/E selectivity in moderate to good yields. Importantly, this copper-catalyzed oxidative cyclization demonstrates a distinctive selectivity in comparison with the related gold catalysis.

I2 -Catalyzed Cycloisomerization of Ynamides: Chemoselective and Divergent Access to Indole Derivatives

Herein, an I₂ -catalyzed unprecedented cycloisomerization of ynamides is developed, furnishing various functionalized bis(indole) derivatives in generally good to excellent yields with wide substrate scope and excellent atom-economy. This protocol not only represents the first molecular-iodine-catalyzed tandem complex alkyne cycloisomerizations, but also constitutes the first chemoselective cycloisomerization of tryptamine-ynamides involving distinctively different C(sp³ )-C(sp³ ) bond cleavage and rearrangement. Moreover, chiral tetrahydropyridine frameworks containing two stereocenters are obtained with moderate to excellent diastereoselectivities and excellent enantioselectivities. Meanwhile, cycloisomerization and aromatization of ynamides produce pyrrolyl indoles with high efficiency enabled by I₂ . Additionally, control experiments and theoretical calculations reveal that this reaction probably undergoes a tandem 5-exo-dig cyclization/rearrangement process.