RhIII-Catalyzed Synthesis of Cyclopenta[b]carbazoles via Cascade C–H/C–C Bond Cleavage and Cyclization Reactions: Using Amide as a Traceless Directing Group

Pd-Catalyzed Selective Arylative Cascade Cyclization of 1,6-Diynes and Dibenzoxaborins for Fused Naphthalene Derivatives

A palladium-catalyzed new mode of cascade arylative cyclization of 1,6-diynes is disclosed using dibenzoxaborin as an arylating agent featuring transmetalation and selective migratory insertion as the key steps. This process enables the efficient construction of polysubstituted fused naphthalene skeletons via the formation of three new C-C bonds through dual regioselectivity in both arylation as well as C-H functionalization. Some control experiments and kinetic isotope effect (KIE) studies were conducted to elucidate the reaction mechanism, and some product diversifications were achieved to showcase the synthetic potential.

Three-component synthesis of N-naphthyl pyrazoles via Rh(III)-catalyzed cascade pyrazole annulation and Satoh-Miura benzannulation

The synthesis of N-naphthyl pyrazoles has been realized by the direct three-component reactions of enaminones, aryl hydrazine hydrochlorides and internal alkynes via Rh(III) catalysis. The synthetic reactions employing simple substrates lead to simultaneous construction of dual cyclic moieties, including a pyrazole ring and a phenyl ring, via sequential formation of two C-N and three C-C bonds.

Indane-1,3-Dione: From Synthetic Strategies to Applications

Indane-1,3-dione is a versatile building block used in numerous applications ranging from biosensing, bioactivity, bioimaging to electronics or photopolymerization. In this review, an overview of the different chemical reactions enabling access to this scaffold but also to the most common derivatives of indane-1,3-dione are presented. Parallel to this, the different applications in which indane-1,3-dione-based structures have been used are also presented, evidencing the versatility of this structure.

Synthesis of 3,3′-bisindoles via demethylenation

This work provides a mild demethylenation for the synthesis of 3,3′-bisindoles.

Rhodium-Catalyzed Regioselective Double Annulation of Enaminones with Propargyl Alcohols: Rapid Access to Arylnapthalene Lignan Derivatives

We present here a rhodium-catalyzed oxidative three-point double annulation of enaminones with propargylic alcohols via a C-H and a C-N bond activation to access arylnaphthalene-based lignan derivatives. The key step in the reaction is the regioselective insertion of propargylic alcohol into the rhoda-cycle, a result of hydroxyl rhodium coordination. Necessary control experiments and KIE studies were conducted to determine the mechanism.

Synthesis of Indole-Fused Oxepines via C-H Activation Initiated Diastereoselective [5 + 2] Annulation of Indoles with 1,6-Enynes

A rhodium-catalyzed diastereoselective formal [5 + 2] annulation of indoles with cyclohexadienone-containing 1,6-enynes has been established via indole 2,3-difunctionalization. The reaction, probably proceeding through tandem indole C2-H alkenylation and intramolecular Friedel-Crafts alkylation relay, provides rapid construction of indole-fused oxepines in good to excellent yields with a broad substrate scope. This method also features concomitant construction of cis-hydrobenzo[b] oxepine scaffolds, a core unit found in numerous natural products of important biological activities.

Synthesis of Cyclopentadienes for Cyclopentadienyl Ligands via Cp*RhIII-Catalyzed Formal sp3 C-H Activation/Spiroannulations

An efficient Cp*Rh^III-catalyzed formal C(sp³)-H activation/spiroannulation of alkylidene Meldrum's acids with alkynes has been developed using catalytical Cu(OAc)₂ and air as the oxidant. This reaction demonstrates a new and straightforward approach to spirocyclopentadienes with Meldrum's acid moieties in good to excellent yields under mild reaction conditions with a broad substrate scope. Notably, this protocol provides a novel and straightforward approach to cyclopentadienes with various substitution patterns and the corresponding cyclopentadienyl-type ligands from simple substrates.

Pd(ii)-Catalyzed enantioconvergent twofold C–H annulation to access atropisomeric aldehydes: a platform for diversity-oriented-synthesis

The first Pd(ii)-catalyzed atroposelective dual C–H annulative strategy for diverse synthesis of functionalized axially chiral biaryls was developed.

Recent Advances on Synthetic Methodology Merging C-H Functionalization and C-C Cleavage

The functionalization of C-H bonds has become a major thread of research in organic synthesis that can be assessed from different angles, for instance depending on the type of catalyst employed or the overall transformation that is carried out. This review compiles recent progress in synthetic methodology that merges the functionalization of C-H bonds along with the cleavage of C-C bonds, either in intra- or intermolecular fashion. The manuscript is organized in two main sections according to the type of substrate in which the cleavage of the C-C bond takes place, basically attending to the scission of strained or unstrained C-C bonds. Furthermore, the related research works have been grouped on the basis of the mechanistic aspects of the different transformations that are carried out, i.e.,: (a) classic transition metal catalysis where organometallic intermediates are involved; (b) processes occurring via radical intermediates generated through the use of radical initiators or photochemically; and (c) reactions that are catalyzed or mediated by suitable Lewis or Brønsted acid or bases, where molecular rearrangements take place. Thus, throughout the review a wide range of synthetic approaches show that the combination of C-H and C-C cleavage in single synthetic operations can serve as a platform to achieve complex molecular skeletons in a straightforward manner, among them interesting carbo- and heterocyclic scaffolds.

Traceless directing groups: a novel strategy in regiodivergent C-H functionalization

The use of functional groups as internal ligands for assisting C-H functionalization, termed the chelation assisted strategy, is emerging as one of the most powerful tools for construction of C-C and C-X bonds from inert C-H bonds. However, there are various directing groups which cannot be either removed after functionalization or require some additional steps or reagents for their removal, thereby limiting the scope of structural diversity of the products, and the step and atom economy of the system. These limitations are overcome by the use of the traceless directing group (TDG) strategy wherein functionalization of the substrate and removal of the directing group can be carried out in a one pot fashion. Traceless directing groups serve as the most ideal chelation assisted strategy with a high degree of reactivity and selectivity without any requirement for additional steps for their removal. The present review overviews the use of various functional groups such as carboxylic acids, aldehydes, N-oxides, nitrones, N-nitroso amines, amides, sulfoxonium ylides and silicon tethered directing groups for assisting transition metal catalyzed C-H functionalization reactions in the last decade.

One-step synthesis of benzo[b]thiophenes by aryne reaction with alkynyl sulfides

An aryne reaction with alkynyl sulfides affording benzo[b]thiophenes is disclosed. A wide range of 3-substituted benzothiophenes were synthesized from easily available o-silylaryl triflates and alkynyl sulfides in a one-step intermolecular manner. The synthesis of diverse multisubstituted benzothiophene derivatives involving a pentacyclic compound was achieved by virtue of the good functional group tolerance and versatile C2 functionalizations.