Functionality-Directed Regio- and Enantio-Selective Olefinic C-H Functionalization of Aryl Alkenes

Aryl alkenes represents one of the most widely occurring structural motif in countless drugs and natural products, and direct C-H functionalization of aryl alkenes provides atom- step efficient access toward valuable analogues. Among them, group-directed selective olefinic α- and β-C-H functionalization, bearing a directing group on the aromatic ring, has attracted remarkable attentions, including alkynylation, alkenylation, amino-carbonylation, cyanation, domino cyclization and so on. These transformations proceed by endo- and exo-C-H cyclometallation and provide aryl alkene derivatives in excellent site- stereo-selectivity. Enantio-selective α- and β- olefinic C-H functionalization were also covered to synthesis axially chiral styrenes.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Transition metal-catalyzed double Cvinyl-H bond activation: synthesis of conjugated dienes

Conjugated dienes have occupied a pivotal position in the field of synthetic organic chemistry and medicinal chemistry. They act as important synthons for the synthesis of various biologically important molecules and therefore, gain tremendous attention worldwide. A wide range of synthetic routes to access these versatile molecules have been developed in the past decades. Transition metal-catalyzed cross-dehydrogenative coupling (CDC) has emerged as one of the utmost front-line research areas in current synthetic organic chemistry due to its high atom economy, efficiency, and viability. In this review, an up-to-date summary including scope, limitations, mechanistic studies, stereoselectivities, and synthetic applications of transition metal-catalyzed double C_vinyl-H bond activation for the synthesis of conjugated dienes has been reported since 2013. The literature reports mentioned in this review have been classified into three different categories, i.e. (a) C_vinyl-C_vinyl bond formation via oxidative homo-coupling of terminal alkenes; (b) C_vinyl-C_vinyl bond formation via non-directed oxidative cross-coupling of linear/cyclic alkenes and terminal/internal alkenes, and (c) C_vinyl-C_vinyl bond formation via oxidative cross-coupling of directing group bearing alkenes and terminal/internal alkenes. Overall, this review aims to provide a concise overview of the current status of the considerable development in this field and is expected to stimulate further innovation and research in the future.

PdII -Catalyzed C(alkenyl)-H Activation Facilitated by a Transient Directing Group

Palladium(II)‐catalyzed C(alkenyl)−H alkenylation enabled by a transient directing group (TDG) strategy is described. The dual catalytic process takes advantage of reversible condensation between an alkenyl aldehyde substrate and an amino acid TDG to facilitate coordination of the metal catalyst and subsequent C(alkenyl)−H activation by a tailored carboxylate base. The resulting palladacycle then engages an acceptor alkene, furnishing a 1,3‐diene with high regio‐ and E/Z‐selectivity. The reaction enables the synthesis of enantioenriched atropoisomeric 2‐aryl‐substituted 1,3‐dienes, which have seldom been examined in previous literature. Catalytically relevant alkenyl palladacycles were synthesized and characterized by X‐ray crystallography, and the energy profiles of the C(alkenyl)−H activation step and the stereoinduction model were elucidated by density functional theory (DFT) calculations.

One-pot two-step dithiocarbamylation of styrenes: metal-free stereoselective synthesis of styrenyl dithiocarbamates

Styrenes have been functionalized to produce styrenyl dithiocarbamates by a one-pot two-step procedure without using any metal catalysts. Styrene was transformed into a bromo-derivative, which undergoes a domino nucleophilic substitution followed by elimination in the presence of a dithiocarbamate anion and triethylamine to produce trans-styrenyl dithiocarbamates exclusively. The reaction shows a wide substrate scope and good yields of products.

Construction of axial chirality by asymmetric alpha C–H alkenylation of aryl alkenes

An asymmetric α-C–H alkenylation of aryl alkenes has been disclosed to provide axially chiral aryl 1,3-dienes, proceeding through six-membered exo-cyclopalladation, assisted by an aldehyde/l-t-leucine derived transient chiral auxiliary.

The cobalt(ii)-catalyzed acyloxylation of picolinamides with bifunctional silver carboxylate via C–H bond activation

The cobalt(ii)-catalyzed C–H bond acyloxylation of picolinamides with bifunctional silver carboxylate has been developed. The mild and practical esterification provides an atom-economic route to access to polysubstituted naphthalene compounds.

Access to axially chiral aryl 1,3-dienes by transient group directed asymmetric C-H alkenylations

We present a Pd-catalyzed atroposelective preparation of aryl 1,3-dienes from readily available styrenes and olefins through aldehyde derived transient chiral auxiliary, proceeding by enantioselective olefinic C-H alkenylation of styrenes via...