Construction of Spironaphthalenones via Gold-Catalyzed Intramolecular Dearomatization Reaction of β-Naphthol Derivatives

Radical Three-Component Nitro Spiro-Cyclization of Unsaturated Sulfonamides/Amides to Access NO2-Featured 4-Azaspiro[4.5]decanes

Free radical three-component nitration/spirocyclization of unsaturated sulfonamides/amides with tert-butyl nitrite was developed for the construction of diverse NO2-revised 4-azaspiro[4.5]decanes. This tandem system featured metal-free participation, simple operation, good selectivity/yields, and a green/low-cost O source. Meanwhile, one nitro-containing complex molecule and a scaled-up operation were performed well to test the synthetic potential of the cascade reaction. Isotopic labeling, radical inhibition experiments, and DFT analysis were carried out to gain insight into the reaction process.

Pd-Catalyzed Asymmetric Annulative Dearomatization of Phenols for Regio- and Enantioselective Synthesis of Spirocyclohexadienones

A palladium-catalyzed asymmetric annulative dearomatization of phenols with butene dicarbonate is reported, enabling twofold decarboxylative allylation to regioselectively produce a range of spirocyclohexadienones with 29-95% yields and 74-99% ee. A catalytic dearomative formal [4 + 2] cyclization of 1,1'-biphenyl-2,4'-diols delivered spiro[chromane-4,1'-cyclohexane]-2',5'-dien-4'-ones with high enantioselectivity, whereas enantioenriched spiro[cyclohexane-1,4'-quinoline]-2,5-dien-4-ones were generated starting from 2'-amino-[1,1'-biphenyl]-4-ols as 1,4-dinucleophiles.

Redox-Neutral Intramolecular Dearomative Spirocyclization of Phenols Induced by Visible Light

Described herein is a redox-neutral intramolecular dearomative spirocyclization induced by visible light. The photochemical cyclization was catalyzed by a phenolate anion-derived photocatalyst and delivered the spirocyclohexadienone. Mechanistic experiments revealed that the aryl halide was reduced to aryl radical via the single-electron transfer (SET) process under visible light irradiation. The electrophilic addition of an aryl radical with the phenolate anion moiety gave a radical anion intermediate, which recycled the photocatalyst by a second SET process.

Nitro-Spirocyclization of Biaryl Ynones with tert-Butyl Nitrite: Access to NO2-Substituted Spiro[5,5]trienones

A metal/peroxide-free involved simple cascade 6-exo-trig spirocyclization of tert-butyl nitrite with biaryl ynones has been finished, which resulted in various NO₂-modified spiro[5,5]trienones with good regioselectivity/yields. A variety of scaled-up experiments, reduction/epoxidation operations, and mechanistic studies were performed to verify the merits and spirocyclization process of this radical system. Finally, the structure of the spirocycles was confirmed by single-crystal X-ray diffraction.

C-O Coupling/[4+2] Cycloaddition Tandem Reactions via Oxidative Dearomatization of BINOLs: Access to Bridged Polycyclic Compounds

Intramolecular C-H activation/C-O coupling, dearomatization, and [4+2] cycloaddition of BINOL units have been well developed in a one-pot approach with maleimide derivatives as the dienophiles. This tandem catalytic system generates a variety of functionalized bridged polycyclic products in a step-economical manner, which greatly enriches the modification methods and strategies for the BINOL skeletons.

Piperidine Derivatives: Recent Advances in Synthesis and Pharmacological Applications

Piperidines are among the most important synthetic fragments for designing drugs and play a significant role in the pharmaceutical industry. Their derivatives are present in more than twenty classes of pharmaceuticals, as well as alkaloids. The current review summarizes recent scientific literature on intra- and intermolecular reactions leading to the formation of various piperidine derivatives: substituted piperidines, spiropiperidines, condensed piperidines, and piperidinones. Moreover, the pharmaceutical applications of synthetic and natural piperidines were covered, as well as the latest scientific advances in the discovery and biological evaluation of potential drugs containing piperidine moiety. This review is designed to help both novice researchers taking their first steps in this field and experienced scientists looking for suitable substrates for the synthesis of biologically active piperidines.

Palladium(0)-Catalyzed Intermolecular Asymmetric Allylic Dearomatization of Substituted β-Naphthols with Morita-Baylis-Hillman (MBH) Adducts

Pd-catalyzed intermolecular asymmetric allylic dearomatization of substituted β-naphthol derivatives with Boc-protected Morita-Baylis-Hillman (MBH) adducts was developed. The reaction occurs smoothly in 1,4-dioxane at room temperature in the presence of [Pd(C₃H₅)Cl]₂ (2.5 mol %), (S, S_p)-PHOX ligand (5.5 mol %), and Li₂CO₃ (1.0 equiv). A series of dearomatized products were afforded in moderate to excellent yields and enantioselectivity (up to 99% yield, 97% ee). Furthermore, the compatibility with gram-scale reaction and mild conditions make the current method synthetically useful.

Regioselective Synthesis of Functionalized Pyrrolo[1,2-a]pyrazine-3,6(2H,4H)-diones via Tandem Post-Ugi Cyclization and Gold(I)-Catalyzed Annulation

A convenient synthesis of less explored pyrrolo[1,2-a]pyrazine-3,6(2H,4H)-diones is described in two steps from Ugi adducts. The method involves acid-mediated cyclization of Ugi adducts to form dihydropyrazinones followed by gold(I)-catalyzed regioselective annulation. The generality of the transformation was established by reacting a variety of substituted dihydropyrazinones under the optimized reaction conditions to form densely functionalized pyrrolo[1,2-a]pyrazine-3,6(2H,4H)-diones in good-to-excellent yields. It was also observed some of the acetone-derived Ugi adducts furnish 7-acyl-pyrroloimidazolones as a byproduct during TFA-mediated cyclization via alkyne-carbonyl metathesis and condensation.

Electrooxidative palladium- and enantioselective rhodium-catalyzed [3 + 2] spiroannulations

Despite indisputable progress in the development of electrochemical transformations, electrocatalytic annulations for the synthesis of biologically relevant three-dimensional spirocyclic compounds has as of yet not been accomplished. In sharp contrast, herein, we describe the palladaelectro-catalyzed C-H activation/[3 + 2] spiroannulation of alkynes by 1-aryl-2-naphthols. Likewise, a cationic rhodium(iii) catalyst was shown to enable electrooxidative [3 + 2] spiroannulations via formal C(sp3)-H activations. The versatile spiroannulations featured a broad substrate scope, employing electricity as a green oxidant in lieu of stoichiometric chemical oxidants under mild conditions. An array of spirocyclic enones and diverse spiropyrazolones, bearing all-carbon quaternary stereogenic centers were thereby accessed in a user-friendly undivided cell setup, with molecular hydrogen as the sole byproduct.

Synthesis of amidines via iron-catalyzed dearomative amination of β-naphthols with oxadiazolones

An efficient and convenient method for the synthesis of amidines bearing a β-naphthalenone moiety catalyzed by cheap iron(ii) chloride is presented by employing oxadiazolones as the nitrene precursors.

Visible Light-Promoted Selenylative Spirocyclization of Biaryl Ynones toward the Formation of Selenated Spiro[5.5]trienones

A visible-light induced dearomative cascade cyclization of biaryl ynones with diselenides under photocatalyst and external additive-free conditions has been explored, giving a series of selenated spiro[5.5]trienones in moderate to good...

Dearomative Cyclopropanation of Naphthols via Cyclopropene Ring-Opening

The dearomatization of 2-naphthols represents a simple method for the construction of complex 3D structures from simple planar starting materials. We describe a cyclopropanation of 2-naphthols that proceeds via cyclopropene ring-opening using rhodium and acid catalysis under mild conditions. The vinyl cyclopropane molecules were formed with high chemoselectivity and scalability, which could be further functionalized at different sites. Both computational and experimental evidence were used to elucidate the reaction mechanism.

Dearomatization reaction of β-naphthols with disulfurating reagents

p-TsOH-catalyzed intermolecular dearomatization reactions of β-naphthols with disulfurating reagents were developed. Various β-naphthalenones bearing a quaternary carbon stereogenic center were obtained smoothly in good to excellent yields with high chemoselectivity in the presence of 5 mol% p-TsOH. This reaction features mild reaction conditions and excellent functional group tolerance.

Asymmetric dearomatization catalysed by chiral Brønsted acids via activation of ynamides

Chiral Brønsted acid-catalysed asymmetric synthesis has received tremendous interest over the past decades, and numerous efficient synthetic methods have been developed based on this approach. However, the use of chiral Brønsted acids in these reactions is mostly limited to the activation of imine and carbonyl moieties, and the direct activation of carbon-carbon triple bonds has so far not been invoked. Here we show that chiral Brønsted acids enable the catalytic asymmetric dearomatization reactions of naphthol-, phenol- and pyrrole-ynamides by the direct activation of alkynes. This method leads to the practical and atom-economic construction of various valuable spirocyclic enones and 2H-pyrroles that bear a chiral quaternary carbon stereocentre in generally good-to-excellent yields with excellent chemo-, regio- and enantioselectivities. The activation mode of chiral Brønsted acid catalysis revealed in this study is expected to be of broad utility in catalytic asymmetric reactions that involve ynamides and the related heteroatom-substituted alkynes.

Enantioselective Friedel-Crafts reaction of hydroxyarenes with nitroenynes to access chiral heterocycles via sequential catalysis

Naphthols, hydroxyindoles and an activated phenol are reacted with differently substituted (E)-nitrobut-1-en-3-ynes using the commercially available Rawal's chiral squaramide. The corresponding β-nitroalkynes were obtained with good yields and excellent enantioselectivities. Moreover, dihydronaphthofurans can be accessed via silver catalysed cyclization in a tandem one-pot procedure, with high preservation of the optical purity.

Gold-Catalyzed Tandem Annulations of Pyridylhomopropargylic Alcohols with Propargyl Alcohols

A gold-catalyzed tandem annulation of propargylic alcohols and pyridylhomopropargylic alcohols is achieved, providing an atom-economical approach to a diverse set of polycyclic dihydrobenzofurans in good yields. The reaction proceeds via the 5-endo-dig cyclization/Meyer-Schuster rearrangement/Friedel-Crafts-type pathway. In this way, three C-C bonds and one C-O bond form to give a polycyclic skeleton in a one-pot process. Moreover, the products exhibit unique optical properties, which reveal their potential application value.