Pd-Catalyzed Rearrangement of N-Alloc-N-allyl Ynamides via Auto-Tandem Catalysis: Evidence for Reversible C-N Activation and Pd(0)-Accelerated Ketenimine Aza-Claisen Rearrangement

Auto tandem triple cascade organocatalysis: access to bis-lactone and butenolide derivatives

The synthesis of bis-lactone and butenolide derivatives was described using alkylidene Meldrum's acid as nucleophiles. The process operates in a triple cascade through an auto tandem catalysis promoted by DBU.

Asymmetric Auto-Tandem Catalysis with Chiral Organosuperbases: Intramolecular Cyclization/Enantioselective Direct Mannich-Type Addition Sequence

An enantioselective addition reaction of alkynyl esters with imines was developed under asymmetric autotandem catalysis with a chiral Brønsted base. A chiral bis(guanidino)iminophosphorane organosuperbase, which has much higher basicity than that of conventional chiral organic bases, efficiently promoted both the intramolecular cyclization for the construction of a benzofuran ring or a benzothiophene ring and the sequential enantioselective direct Mannich-type reaction of diarylmethane derivatives, affording enantio-enriched diarylalkane derivatives that are otherwise difficult to access.

Chemoselectivity of the CuAAC/Ring Cleavage/Cyclization Reaction between Enaminones and α-Acylketenimine

Ketenimines represent an important class of reactive species, useful synthetic intermediates, and synthons. However, in general, ketenimines preferentially undergoes nucleophilic addition reactions with hydroxyl and amino groups, and carbon functional groups remain a less studied subset of such systems. Herein, we develop a straightforward syntheses of pyridin-4(1H)-imines that is achieved by cyclization of a reacting enaminone unit with α-acylketenimine which is generated from the reactions of sulfonyl azides and terminal ynones in situ (CuAAC/Ring cleavage reaction). The cascade process preferentially starts with the nucleophilic α-C of the enaminone unit instead of an amino group, attacking the electron-deficient central carbon of ketenimine, and the chemoselectivity unconventional products pyridin-4(1H)-imines were formed by intramolecular cyclization.

Asymmetric Auto-Tandem Palladium Catalysis for 2,4-Dienyl Carbonates: Ligand-Controlled Divergent Synthesis

Developing new asymmetric auto-tandem catalysis processes, especially in a divergent manner, is highly attractive but extremely challenging. Presented herein is a palladium-catalyzed auto-tandem reaction between 2,4-dienyl carbonates and o-TsNH arylimines or trifluoroacetophenones that proceeds through a consecutive N-allylation, vinylogous addition, π-σ-π isomerization, and another N-allylation sequence. Importantly, switchable diastereodivergent synthesis could be achieved by tuning the chiral bisphosphine ligands, which led to the construction of a broad spectrum of fused tetrahydroquinoline architectures with moderate to excellent enantioselectivity. Ligand control even enabled effective access to regiodivergent azetidine or chemodivergent β-H elimination with fair enantioselectivity, further showing the versatility of the current auto-tandem catalysis.

Recent Advances in Catalytic [3,3]-Sigmatropic Rearrangements

Carbon–carbon bond formation by [3,3]-sigmatropic rearrangement is a fundamental and powerful method that has been used to build organic molecules for a long time. Initially, Claisen and Cope rearrangements proceeded at high temperatures with limited scopes. By introducing catalytic systems, highly functionalized substrates have become accessible for forming complex structures under mild conditions, and asymmetric synthesis can be achieved by using chiral catalytic systems. This review describes recent breakthroughs in catalytic [3,3]-sigmatropic rearrangements since 2016. Detailed reaction mechanisms are discussed to enable an understanding of the reactivity and selectivity of the reactions. Finally, this review is inspires the development of new cascade reaction pathways employing catalytic [3,3]-sigmatropic rearrangement as related methodologies for the synthesis of complex functional molecules.

Radical Chain Isomerization of N-Sulfonyl Ynamides to Ketenimines and Its Application to Furan Dearomatization

A radical chain isomerization of N-sulfonyl ynamides to isolable ketenimines is developed, featuring mild reaction conditions, a high efficiency, ∼100% atom economy, a broad substrate scope, and column chromatography-free workup in most cases. Meanwhile, an unprecedented dearomatization of furans is achieved by the radical chain isomerization-triggered aza-Claisen rearrangement, providing highly chemo-, regio-, stereo-, and diastereoselective access to functionalized quaternary nitriles.

Media-Driven Pd-Catalyzed Reaction Cascades with 1,3-Diynamides Leading Selectively to Either Indoles or Quinolines

Divergent Pd-catalyzed reaction cascades with various 1,3-diynamides yielding either 2-amino-3-alkynylindoles or 2-amino-4-alkenylquinolines were established. Omitting or adding TBAF (tetrabutylammonium fluoride) to the reaction of N,N-(2-iodophenyl)(4-toluenesulfonyl)-1,3-diynamides with secondary or primary amines in the presence of KOH in THF and catalytic amounts of Pd(PPh₃ )₄ completely changed the outcome of the reaction. In the absence of TBAF, 2-amino-3-alkynylindoles were the sole products, while the presence of TBAF switched the product formation to 2-amino-4-alkenylquinolines. Deuterium labeling proceeded selectively at the C3 and C11 positions of the 2-amino-4-alkenylquinoline products and this suggests the unprecedented formation of [4]cumulenimines from 1,3-diynamides as reactive key intermediates.

Synthesis of polysubstituted azetidines via cascade trifluoromethylation/cyclization of N-allyl ynamides

A cascade trifluoromethylation/cyclization of N-allyl sulfonylynamides is developed, providing a direct access to azetidine-fused tricyclic compounds at room temperature.

Nonmetal-catalyzed hydroamination of ynamides with amines

A TfOH-catalyzed hydroamination of ynamides with primary and secondary amines under mild reaction conditions is described for the efficient synthesis of N-arylimines and ethene-1,1-diamines.