Rhodium-Catalyzed C–H Bond Activation/[4 + 2] Annulation/Aromatization Cascade To Produce Phenol, Naphthol, Phenanthrenol, and Triphenylenol Derivatives

Access to Naphthoic Acid Derivatives through an Oxabenzonorbornadiene Rearrangement

Herein, the synthesis of 1-hydroxy-2-naphthoic acid esters through an unexpected Lewis-acid-mediated 1,2-acyl shift of oxabenzonorbornadienes is reported. Using this methodology, novel substitution patterns for 1-hydroxy-2-naphtoic acid esters can be obtained. A mechanistic proposal and rationale for this transformation, the products of which had been previously incorrectly characterized, is given.

Recent progress in metal assisted multicomponent reactions in organic synthesis

To prepare complicated organic molecules, straightforward, sustainable, and clean methodologies are urgently required. Thus, researchers are attempting to develop imaginative approaches. Metal-catalyzed multicomponent reactions (MCRs) offer optimal molecular diversity, high atomic efficiency, and energy savings in a single reaction step. These versatile protocols are often used to synthesize numerous natural compounds, heterocyclic molecules, and medications. Thus far, the majority of metal-catalyzed MCRs under investigation are based on metal catalysts such as copper and palladium; however, current research is focused on developing novel, environmentally friendly catalytic systems. In this regard, this study demonstrates the effectiveness of metal catalysts in MCRs. The aim of this study is to provide an overview of metal catalysts for safe application in MCRs.

Ring Expansion of 1-Indanones to 2-Halo-1-naphthols as an Entry Point to Gilvocarcin Natural Products

Herein, we describe a two-step ring expansion of 1-indanones to afford 2-chloro/bromo-1-naphthols (32 examples). The developed method shows broad functional group tolerance, benefits from mild reaction conditions, and enables rapid access to the tetracyclic core of gilvocarcin natural products. The orthogonally functionalized products allow for selective postmodifications as exemplified in the total synthesis of defucogilvocarcin M. For the selective oxidation of the chromene, a mild and regioselective oxidation protocol (DDQ and TBHP) was developed.

Transition-metal-free oxidative cyclization reaction of enynals to access pyrane-2-one derivatives

A novel and efficient metal-free C-H functionalization of enynals is developed to synthesize α-pyrone derivatives via the formation of two C-O bonds. In this project, K₂S₂O₈ has been introduced as an efficient oxygen source and C-H functionalization agent in regioselective oxidative cyclization reaction with a relatively broad substrate scope.

Copper-catalyzed synthesis of phenol and diaryl ether derivatives via hydroxylation of diaryliodoniums

A copper-catalysed hydroxylation of diaryliodoniums to generate phenols and diaryl ethers is reported. This method allows the synthesis of diversely functionalized phenols under mild reaction conditions without the need for a strong inorganic base or an expensive noble-metal catalyst. Significantly, convenient application of diaryliodoniums is demonstrated in the preparation of diaryl ethers in a one-pot operation.

Copper-Catalyzed Cascade Aminoalkynylation-Oxidation of Propargylic Alcohols: Stereospecific Synthesis of ( Z)-2-Amino Conjugated Enynals/Enynones

Copper-catalyzed cascade aminoalkynylation-oxidation of propargylic alcohols has been realized, sterospecifically providing an array of ( Z)-2-amino conjugated enynals/enynones in good yields under mild conditions. This transformation involves a rare 1,3-alkynyl migration of propargylic alcohols and simultaneously forms C-C, C-N, and C═O bonds. Furthermore, ( Z)-2-amino conjugated enynals were applied to efficiently synthesize 3,5-disubstituted-1 H-pyrrole-2-carbaldehyde and conjugated enynol derivatives.

Rhodium-Catalyzed Asymmetric [2 + 2 + 2] Cycloaddition of Unsymmetrical α,ω-Diynes with Acenaphthylene

It has been established that a cationic rhodium(I)/(R)-BINAP complex catalyzes the asymmetric [2 + 2 + 2] cycloaddition of unsymmetrical α,ω-diynes with acenaphthylene at room temperature to give the corresponding chiral multicyclic compounds with high yields and ee values. Interestingly, enantioselectivity highly depended on the structures of α,ω-diynes used. The structural requirements of α,ω-diynes for high enantioselectivity were opposite to those in our previously reported cationic rhodium(I)/(R)-Difluorphos complex-catalyzed asymmetric [2 + 2 + 2] cycloaddition of α,ω-diynes with indene.

Palladium meets copper: one-pot tandem synthesis of pyrido fused heterocycles via Sonogashira conjoined electrophilic cyclization

An efficient step-economical tandem approach for the direct synthesis of pyrido fused indole, quinoline, benzofuran and benzothiophene derivatives using a bimetallic Pd/Cu catalytic system has been described. The three component reaction of o-halo aldehydes, alkynes and tert-butylamine leads to the synthesis of biologically active polyheterocycles. The present strategy involves the dual role of tert-butylamine and copper(i) in Sonogashira coupling followed by electrophilic cyclization through imine formation. The chemistry has been validated by X-ray crystallographic studies.

Synthesis of multisubstituted phenols by formal [4 + 2] cycloaddition of nucleophilic alkynes with 3-ethoxycyclobutanones

Formal [4 + 2] cycloaddition between 3-ethoxycyclobutanones and nucleophilic alkynes proceeded to give multisubstituted phenols by using TiCl₄ as a Lewis acid.

Ruthenium(0)-Catalyzed [4+2] Cycloaddition of Acetylenic Aldehydes with α-Ketols: Convergent Construction of Angucycline Ring Systems

Ruthenium(0) complexes modified by CyJohnPhos or RuPhos catalyze the successive C-C coupling of acetylenic aldehydes with α-ketols to form [4+2] cycloadducts as single diastereomers. This method enables convergent construction of type II polyketide ring systems of the angucycline class.

Rhodium(iii)-catalyzed C–H alkynylation of azomethine ylides under mild conditions

Rh(iii) complexes catalyzed the ortho C–H alkynylation of azomethine imine, which acts as a masked aldehyde group.