Palladium-Mediated Remote Functionalization in γ- and ε-Arylations and Alkenylations of Unblocked Cyclic Enones

A Sequential Transition Metal and Organocatalytic Approach to the Enantioselective Synthesis of C2-Spiroindoline Systems

We report herein an organocatalyzed enantioselective spirocyclization strategy to access valuable C2-spiroindoline scaffolds bearing a quaternary stereocenter via an aza-Michael addition reaction, wherein the acid additive plays the role of dual functionality. The substrates for this key step were put together by an exo-selective, Pd-catalyzed γ-arylation of silyldienol ethers of the corresponding cyclohexenones. A close alliance between a low catalyst loading and a slow reaction rate yields C2-spiroindolines with good enantioselectivity.

Cu/Pd-catalyzed arylboration of a 1-silyl-1,3-cyclohexadiene for stereocontrolled and diverse cyclohexane/ene synthesis

The synthesis and Cu/Pd-catalyzed arylboration of 1-silyl-1,3-cyclohexadiene is described. This diene is significant as it allows for synthesis of polyfunctional cyclohexane/enes. To achieve high levels of diastereoselectivity, the use of a pyridylidene Cu-complex was employed. In addition, through the use of a chiral catalyst, an enantioselective reaction was possible. Due to the presence of the silyl and boron substituents, the products can be easily diversified into a range of valuable cyclohexane/ene products.

Examining the Scope of Deriving β-Aryl Enones from Enol Silanes as Ketone Equivalents via Pd(II)-Mediated Sequential Dehydrosilylation and Arylation

Silyl enol ethers were examined as a masked source of saturated ketones to derive β-aryl enones and their derivatives by dehydrosilylation to generate enones in situ and subsequent oxidative arylation with arylboronic acids as transmetallation coupling partners using relayed Pd(II) catalysis in one pot under base-free conditions. Oxygen was found to be an efficient and green oxidant to enable both dehydrosilylation of enol silanes and arylation. Additionally, arylation conditions can be custom-designed to take advantage of aryl halides as an alternative source of arylating agents. The preparative scope was investigated with 35 examples (up to 95% yield), and mechanistic studies implied a cationic Pd(II)-based catalytic system.

Protecting-Group-Free Total Synthesis of Anticancer (±)-Melotenine A

Melotenine A, isolated from Melodinus tenuicaudatus, possesses significant anticancer activity against several human cancer cell lines. The synthesis of (±)-melotenine A was achieved without the use of any protecting groups in 11 steps with an overall yield of 6.7%. The key steps of our strategy were a Diels–Alder reaction to construct the tetracyclic framework and ring-closing metathesis to form the seven-membered ring of (±)-melotenine A.

Palladium-Catalyzed Site-Selective Arylation of α,β-Unsaturated Carbonyl Compounds through a Ligand-Controlled Strategy

Palladium-catalyzed direct arylation of α,β-unsaturated carbonyl compounds is an efficient and attractive strategy to access arylated α,β-unsaturated carbonyl compounds through the construction of carbon–carbon bonds. This reaction has several challenges, especially in terms of the control of regioselectivity between α- and γ-arylation and the selectivity for monoarylation and multiple arylation. Herein, we discuss the recent development of γ-arylation of α,β-unsaturated carbonyl compounds and present the ligand-controlled, site-selective α- and γ-arylation of α,β-unsaturated carbonyl ketones with (hetero)aryl halides. The site selectivity of the reaction is switchable by simply changing the phosphine ligand.

1 Introduction

2 Reaction Development and Mechanistic Investigation

3 Conclusion and Outlook

Synthesis of N-substituted quaternary carbon centers through KOt-Bu-catalyzed aza-Michael addition of pyrazoles to cyclic enones

This study reports an effective and mild protocol for the construction of N-substituted quaternary carbon centers via the KOt-Bu-catalyzed aza-Michael addition of pyrazoles with β-substituted cyclic enones.

Palladium-Catalyzed Direct γ-C(sp3)-H Arylation of β-Alkoxy Cyclohexenones: Reaction Scope and Mechanistic Insights

Direct γ-C(sp3)-arylation of unactivated electron-rich enones is a long-standing challenge. Herein, we report a mild Pd-catalyzed method for direct γ-C(sp3)-arylation of various unactivated β-alkoxy cyclohexenones. The method is not only...

Palladium-catalyzed functionalizations of acidic and non-acidic C(sp3)-H bonds - recent advances

A tremendous upsurge has been seen in the recent decade for the proximal and remote functionalization of activated and unactivated substrates via palladium redox pathways. This feature article discusses some of the recent reports on direct as well as indirect C(sp3)-H functionalization via cross-coupling reactions under palladium catalysis. Activated substrates (possessing acidic C(sp3)-H) including enones, ketones, aldehydes, silylenol ethers, esters, silyl ketene acetals, amides, cyano, α-amino esters, and O-carbamates, capable of undergoing cross-coupling reactions at the α-, β-, γ-, δ- and ε-positions, will be discussed. To overcome the challenging task of achieving regioselectivity, a variety of innovative modifications have been reported. The reports of C-H activations based on directing group, and as native functionality have been illustrated at the β-, γ- and δ-positions. Substrates such as α-amino esters, carbonyls, carboxylic acids and their derivatives, afford site-selective C(sp3)-H functionalization via varied-sized reactive metallacycles and are a unique class of substrates whose C(sp3)-H functionalizations were earlier considered as very difficult.