A Facile Access to 4‑Substituted-2-naphthols via a Tandem Friedel–Crafts Reaction: A β‑Chlorovinyl Ketone Pathway

A one-pot synthesis of 2-naphthol derivatives is accomplished using a tandem Friedel–Crafts reaction sequence. The developed methodology allows for a concomitant construction of up to three C–C bonds between readily available alkynes and phenylacetyl chloride derivatives by an intermolecular Friedel–Crafts acylation of alkynes followed by an intramolecular Friedel–Crafts alkylation of β-chlorovinyl ketone intermediates

A One-Pot Synthesis of Pyranone and Pyrrole Derivatives from β‑Chlorovinyl Ketones via Direct Conjugate Addition Approach

The direct conjugate addition reactions of imino esters to β-chlorovinyl ketones have been accomplished in the presence of a substoichiometric amount of hard base, LiHMDS. An <i>in situ</i> generated species from the conjugate addition reaction readily acted as autocatalyst to convert the imino esters to its corresponding enolates. By utilizing a sequence of conjugate addition/elimination/lactonization followed by either reduction or reaction with amines, the novel one-pot syntheses of highly functionalized pyranone and pyrrole derivatives were accomplished in good to excellent yields

1,3-Dienones and 2<i>H</i>‑Pyran-2-ones from Soft α‑Vinyl Enolization of β‑Chlorovinyl Ketones: Defined Roles of Brönsted and Lewis Base

The eliminative reaction pathways of (<i>E</i>)-β-chlorovinyl ketones were investigated in the presence of both Brönsted and Lewis bases. The Brönsted base, Et₃N, effected the soft α-vinyl enolization of (<i>E</i>)-β-chlorovinyl ketones to [3]­cumulenol intermediates; in turn, a catalytic amount of Lewis base, PPh₃, initiated isomerization to provide 1,3-dienones in high yields. The introduction of a carbon-based nucleophile into the reaction mixture provided the highly efficient synthetic route to 2<i>H</i>-pyran-2-ones in one pot, where the carbon-based nucleophile generated by an extra equivalent of Brönsted base, Et₃N, attacked the electrophilic [3]­cumulenol intermediates to initiate cyclization to give 2<i>H</i>-pyran-2-ones

One-Pot Tandem Nickel-Catalyzed α‑Vinyl Aldol Reaction and Cycloaddition Approach to [1,2,3]Triazolo[1,5‑<i>a</i>]quinolines

A one-pot tandem approach to [1,2,3]triazolo[1,5-a]quinolines was developed from (E)-β-chlorovinyl ketones and 2-azidoaryl carbonyls using a sequence of α-vinyl aldol and azide–alkyne cycloaddition reactions. In particular, the intramolecular azide–alkyne cycloaddition of allenol intermediates was readily promoted by a synergistic action of NEt3 and nickel catalysts. Given that the [1,2,3]triazolo[1,5-a]quinolines are useful synthetic precursors to α-diazoimines through ring–chain isomerization process, the subsequent denitrogenative transformations should provide ready access to valuable heterocyclic compounds

Silver-Catalyzed Asymmetric Desymmetrization of Cyclopentenediones via [3 + 2] Cycloaddition with α‑Substituted Isocyanoacetates

A highly selective and practical asymmetric Ag­(I) catalyst system has been developed for the [3 + 2] cycloaddition reactions between isocyanoacetates and cyclopentenediones. The current Ag­(I) catalyst system tolerates moisture and air and readily utilizes class III solvents such as EtOAc and acetone. The development of <i>on demand</i> generation of an active chiral catalyst in the presence of isocyanides paves a way to the efficient asymmetric preparation of bicyclic pyrrolidines with four stereogenic centers, including two quaternary centers in 80–97% ee

<i>o</i>‑Naphthoquinone-Catalyzed Aerobic Oxidation of Amines to (Ket)imines: A Modular Catalyst Approach

A modular aerobic oxidation of amines to imines has been achieved using an <i>ortho</i>-naphtho­quinone (<i><b>o</b></i><b>-NQ</b>) catalyst. The cooperative catalyst system of <i><b>o</b></i><b>-NQ</b> and Cu­(OAc)₂ enabled the formation of homocoupled imines from benzylamines, while the presence of TFA helped the formation of cross-coupled imines in excellent yields. The current mild aerobic oxidation protocol could also be applied to the oxidation of secondary amines to imines or ketimines with the help of cocatalyst, Ag₂CO₃, with excellent yields

Direct Acyl Radical Addition to 2<i>H</i>‑Indazoles Using Ag-Catalyzed Decarboxylative Cross-Coupling of α‑Keto Acids

A direct acyl radical addition to 2<i>H</i>-indazoles has been achieved for the first time, where the less-aromatic <i>quinonoid</i> 2<i>H</i>-indazoles readily accepted radical species to the C-3 position. Motivated by the lack of direct acylation strategy for 2<i>H</i>-indazoles, the current method utilizes the radical acceptability of 2<i>H</i>-indazoles, discovering an ambient temperature reaction to provide facile access to a diverse array of 3-acyl-2<i>H</i>-indazoles with three points of structural diversification in 25%–83% yields

Substituted Pyrrololactams via Ring Expansion of Spiro‑2<i>H</i>‑pyrroles from Intermolecular Alkyne–Isocyanide Click Reactions

The facile synthesis of 6- to 8-membered pyrrololactams has been developed using a ring expansion of spiro-2<i>H</i>-pyrroles, the products of intermolecular alkyne–isocyanide click reactions. The key to successful ring expansion of spiro-2<i>H</i>-pyrroles to pyrrololactams is the enforced orbital overlap between the internal alkene and the amide carbonyl group through the conformationally locked bicyclic structures. The newly disclosed α-isocyano lactams, substrates for click reactions, should find their utility in the synthesis of pharmaceutically important heterocyclic compounds

Unified Approach to (Thio)chromenones via One-Pot Friedel–Crafts Acylation/Cyclization: Distinctive Mechanistic Pathways of β‑Chlorovinyl Ketones

A facile synthetic method to chromenones and thiochromenones has been developed using a one-pot Friedel–Crafts acylation of alkynes with suitably substituted benzoyl chlorides. This unified approach to (thio)­chromenones is readily applicable to aryl- and alkylalkynes where the stereochemically well-defined β-chlorovinyl ketone intermediates undergo distinctively different cyclization pathways. The ready availability of both starting materials, alkynes and benzoyl chlorides, coupled with the experimental simplicity makes the current synthetic method to (thio)­chromenones fast, efficient, and practical

Palladium-Catalyzed Aerobic Oxidative Hydroamination of Vinylarenes Using Anilines: A Wacker-Type Amination Pathway

A palladium-catalyzed intermolecular hydroamination of vinylarene derivatives using anilines has been developed for the first time under aerobic conditions, where the regioselective formation of <i>N</i>-arylketimines is accomplished. The current aerobic <i>oxidative</i> hydroamination pathway of anilines is distinct from that of palladium-catalyzed hydroamination reactions that proceed to give <i>sec</i>-arylethylamine and arylethylamine derivatives, identifying a longstanding missing reaction pathway, Wacker-type amination, to <i>N</i>-arylketimines using anilines. The ready availability of both starting materials, vinylarenes and anilines, offers an attractive and facile synthetic route to <i>N</i>-arylketimines in good to excellent yields