Ruthenium-catalyzed cycloaddition of propargylic alcohols with phenol derivatives via allenylidene intermediates: catalytic use of the allenylidene ligand as the C(3) unit

Intramolecular Copper-Catalyzed Asymmetric Propargylic [4 + 2]- Cycloaddition toward Optically Active Tetrahydroisoindolo[2,1-a]quinoxalines

An intramolecular Cu-catalyzed asymmetric propargylic [4 + 2] cycloaddition of bis-N-nucleophile-functionalized propargylic esters has been realized in the support of a chiral tridentate N-ligand, (S,S)-Pybox-diOAc, leading to chiral tetrahydroisoindolo[2,1-a]quinoxalines in high yields and with good to excellent enantioselectivities. The reaction features high efficiency, simplicity, and broad substrate scope, thus providing a powerful and concise strategy for stereoselective access to optically active polycyclic heterocycle frameworks that are otherwise difficult to synthesize.

Flexible Approach for the Synthesis of Annulated 4H-Pyrans Based on a Cu(I)-Catalyzed C-Allylation/O-Vinylation Reaction of Cyclic 1-Bromoallyl Tosylates with Cyclic and Acyclic 1,3-Dicarbonyls

The Cu(I)-catalyzed reaction between five-, six-, seven-, and eight-membered cyclic 1-bromoallyl tosylates and five- and six-membered cyclic 1,3-dicarbonyls in DMF at 80 °C using Cs₂CO₃ as a base and 2-picolinic acid as an additive selectively delivers a wide array of bisannulated 4H-pyrans in a single step with yields up to 92%. The transformations are considered to proceed as intermolecular C-allylations/intramolecular O-vinylations. With six-membered cyclic 1-bromoallyl tosylates and acyclic β-ketoesters as substrates, the corresponding 5,6,7,8-tetrahydro-4H-chromene-3-carboxylates are obtained with yields up to 59%.

Synthesis of pyrano[3,2-c]quinolones and furo[3,2-c]quinolones via acid-catalyzed tandem reaction of 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described. Depending mainly on the propargylic alcohol used, these tandem reactions proceed via either a Friedel–Crafts-type allenylation followed by 6-endo-dig cyclization sequence to form pyrano[3,2-c]quinolones or a Friedel–Crafts-type alkylation and 5-exo-dig ring closure sequence to afford furo[3,2-c]quinolones in moderate-to-high yields. The pyrano[3,2-c]quinolones products could be further transformed to tetracyclic 4,9-dihydro-5H-cyclopenta[lmn]phenanthridin-5-one derivatives.

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described.

Transition-metal-catalyzed ortho-selective C-H functionalization reactions of free phenols

Phenols are important readily available chemical feedstocks and versatile synthetic building blocks for diverse synthetic transformations. Their motifs are prevalent in a diverse array of natural products, pharmaceuticals, functional materials, and privileged chiral ligands. Consequently, the development of facile and direct site-selective C-H bond functionalization of free phenols is of great importance and considerable interest to both industry and academic research. Over the past decades, transition-metal-catalyzed C-H bond functionalization has become as a powerful synthetic tool in organic synthesis. In this review, we provide a brief overview of recent progress in the transition-metal-catalyzed direct ortho-selective C-H functionalization of free phenols.

Enantioselective Copper-Catalyzed [3 + 3] Cycloaddition of Tertiary Propargylic Esters with 1H-Pyrazol-5(4H)-ones toward Optically Active Spirooxindoles

A copper-catalyzed enantioselective [3 + 3] cycloaddition of 3-ethynyl-2-oxoindolin-3-yl acetates with 1H-pyrazol-5(4H)-ones for the construction of optically active spirooxindoles bearing a spiro all-carbon quaternary stereocenter has been realized. With a combination of Cu(OTf)₂ and chiral tridentate ketimine P,N,N-ligand as the catalyst, the reaction displayed broad substrate scopes, good yields, and high enantioselectivities. This represents the first catalytic asymmetric propargylic cycloaddition with tertiary propargylic esters as the bis-electrophiles for access to chiral spirocyclic frameworks.

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis.

Ligand-controlled regiodivergent π-allyl palladium catalysis enables a switch between [3+2] and [3+3] cycloadditions

Reported herein is the use of ligands to tune the regioselectivity and reactivity of palladium-catalyzed [3+2] and [3+3] cycloadditions.

A simple green protocol for the synthesis of ethyl 3-amino-1-aryl-1H-benzo[f] chromene-2-carboxylates in aqueous media

An eco-friendly and efficient straightforward method has been developed for the synthesis of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate derivatives via 1,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed cyclisation of β-naphthol and 3-aryl-2-cyanoacrylates using water as a green solvent. All products precipitated from the reaction mixture and were isolated by simple filtration. No further work-up nor purification was necessary. The structure of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate was further confirmed by X-ray single crystal analysis.

Synthesis of Organofluoro Compounds Using Methyl Perfluoroalk-2-ynoates as Building Blocks

This review provides an overview of several synthetic applications of methyl perfluoroalk-2-ynoates, leading to convenient preparation of many perfluoroalkylated compounds. The use of these important substrates in the synthesis of various five-, six-, and seven-membered heterocycles, cyclopentadienes, and biphenyls is described, alongside a discussion of the mechanistic aspects of these reactions.

Regioselective, cascade [3+2] annulation of β-naphthols (resorcinols) with Z-enoate propargylic alcohols: a novel entry for the synthesis of complex naphtho(benzo)furans

An unprecedented regioselective, first cascade [3+2] annulation process has been reported between propargylic alcohols and β-naphthols (resorcinols) for the synthesis of naphtho(benzo)furans.

Diversity-oriented synthesis of chromenes via metal-free domino reactions from ketones and phenols

Functionalized chromenes have been synthesized via highly selective metal-free domino reactions from ketones and phenols. 2H-Chromenes, 4H-chromenes, spiran and benzocyclopentane can be respectively prepared starting from the corresponding cyclic ketones, aryl methyl ketones, acetone, and 3-pentanone.