Palladium(II)-Catalyzed Oxidative Cascade Cyclization Reactions of Anilides and Anilines: Scope and Mechanistic Investigations

Palladium-Catalyzed Aminocyclization-Coupling Cascades: Preparation of Dehydrotryptophan Derivatives and Computational Study

Dehydrotryptophan derivatives have been prepared by palladium-catalyzed aminocyclization-Heck-type coupling cascades starting from o-alkynylaniline derivatives and methyl α-aminoacrylate. Aryl, alkyl (primary, secondary, and tertiary), and alkenyl substituents have been introduced at the indole C-2 position. Further variations at the indole benzene ring, as well as the C-2-unsubstituted case, have all been demonstrated. In the case of C-2 aryl substitution, the preparation of the o-alkynylaniline substrate by Sonogashira coupling and the subsequent cyclization–coupling cascade have been performed in a one-pot protocol with a single catalyst. DFT calculations have revealed significant differences in the reaction profiles of these reactions relative to those involving methyl acrylate or methacrylate, and between the reactions of the free anilines and their corresponding carbamates. Those calculations suggest that the nature of the alkene and of the acid HX released in the HX/alkene exchange step that precedes C–C bond formation could be responsible for the experimentally observed differences in reaction efficiencies.

20 Years of Forging N-Heterocycles from Acrylamides through Domino/Cascade Reactions

Acrylamides are versatile building blocks that are easily obtained from readily available starting materials. During the last 20 years, these valuable substrates bearing a nucleophilic nitrogen atom and an electrophilic double bond have proven to be efficient domino partners, leading to a wide variety of complex aza-heterocycles of synthetic relevance. In this non-exhaustive review, metal-free and metal-triggered reactions followed by an annulation will be presented; these two approaches allow good modulation of the reactivity of the polyvalent acrylamides.

1 Introduction

2 Metal-Free Annulations

2.1 Domino Reactions Triggered by a Michael Addition

2.2 Domino Reactions Triggered by an Aza-Michael Addition

2.3 Domino Processes Triggered by an Acylation Reaction

2.4 Domino Reactions Triggered by a Baylis–Hillman Reaction

2.5 Cycloadditions and Domino Reactions

2.6 Miscellaneous Domino Reactions

3 Metal-Triggered/Mediated Annulations

3.1 Zinc-Promoted Transformations

3.2 Rhodium-Catalyzed Functionalization/Annulation Cascades

3.3 Cobalt-Catalyzed Functionalization/Annulation Cascades

3.4 Ruthenium-Catalyzed Functionalization/Annulation Cascades

3.5 Iron-Catalyzed Functionalization/Annulation Cascades

3.6 Palladium-Catalyzed Functionalization/Annulation Cascades

3.7 Copper-Catalyzed Transformations

3.8 Transition Metals Acting in Tandem in Domino Processes

4 Radical Cascade Reactions

5 Conclusion

Recent advances in the catalytic cyclopropanation of unsaturated compounds with diazomethane

The main achievements and development trends of the past 10–15 years related to the catalytic cyclopropanation of unsaturated compounds with diazomethane are integrated and analyzed. The attention is focused on the most efficient catalysts based on palladium compounds. Data on the effects of substrate structure and nature of catalyst components on the regio- and stereoselectivity of these reactions are systematized. Characteristic features of safe methods for diazomethane generation are considered, including the use of membrane technologies and continuous-flow and in situ preparation methods, which have prospects for industrial application.

The bibliography includes 281 references.

Palladium-Catalyzed Stereoselective Aza-Wacker-Heck Cyclization: One-Pot Stepwise Strategy toward Tetracyclic Fused Heterocycles

Palladium-catalyzed intramolecular tandem cyclization reactions were conducted for the synthesis of densely cis/cis-fused aza-tetracyclic structures. The process involved a palladium(II)-catalyzed aerobic aza-Wacker reaction, followed by a palladium(0)-catalyzed Heck reaction. The effects of the solvent and benzene substitution pattern on the one-pot, two-step cascade reaction were studied systematically, and a probable mechanism was proposed. Strained pentahydrobenzo[f]cyclopenta[hi]indolizin-6-one and racemic γ-lycorane can also be synthesized rapidly using this palladium-catalyzed aza-Wacker-Heck cyclization reaction.

PdII -Catalyzed Oxidative Tandem aza-Wacker/Heck Cyclization for the Construction of Fused 5,6-Bicyclic N,O-Heterocycles

A PdII -catalyzed oxidative tandem cyclization was developed for the construction of fused 5,6-bicyclic N, O-heterocycles. This reaction was enabled by the combined use of a 3-methylpyridine ligand and pentafluorobenzoic acid additive. A range of heterocyclic products with different substituents could be prepared in moderate to good yields via this methodology. Several transformations, including a scaled-up preparation of product 2 a, were also carried out showing the good applicability of our methodology.

Pd-Catalyzed Intramolecular Aminoalkylation of Unactivated Alkenes: Access to Diverse N-Heterocycles

A highly efficient palladium-catalyzed intramolecular aminoalkylation of unactivated alkenes in the absence of an external ligand and oxidant is described. New C-N and C(sp³)-C(sp³) bonds are formed simultaneously. This general transformation allows for construction of diverse N-heterocycles. Mechanistic studies show that the process may involve a four-membered Pd(alkyl)amido intermediate.

On the regiochemical differences between Pd-catalyzed heterocyclization–allylation and –arylation reactions of alkynylbenzamides: preparation of 4-allyl-isochromen-1-imines and computational study

The divergent regioselectivity of allylation and arylation of 2-alkynylbenzamides under Pd(0)-catalyzed conditions is studied with the aid of DFT calculations.

Palladium(II)-catalyzed intramolecular tandem aminoalkylation via divergent C(sp3)-H functionalization

We have developed a Pd(II)-catalyzed oxidative tandem aminoalkylation via divergent C(sp(3))-H functionalization, affording three- and five-membered-ring fused indolines in good yields under two optimized conditions, respectively. The mechanism studies have indicated that the benzylic C-H cleavage involved in the former transformation is the rate-determining step, while the cleavage of amide α-C-H in the latter is not. This is the first example of a Pd-catalyzed tandem reaction involving C(sp(3))-H activation without the employment of prefunctionalized reagents (e.g., halogenated and boron reagents) and directing groups, representing a green and economic protocol for the construction of N-containing heterocycles.

Highly enantioselective oxidative tandem cyclization reaction: a chiral ligand and an anion cooperatively control stereoselectivity

The unprecedented combination of a palladium(ii) complex with a chiral Bu-QUOX ligand and a chiral phosphoric acid enables the highly efficient asymmetric oxidative tandem cyclization reaction, providing a straightforward method to access chiral 6,5-bicyclic aza-heterocycles in moderate to good yields and with excellent enantioselectivities.