Catalytic Three-Component Synthesis of Functionalized Naphtho[2,1-b]oxecines via a Double Bond Cleavage–Rearrangement Cascade

Olefin skeletal rearrangement enabling access to multiarylated N-sulfonyl amidines

A base-promoted olefin skeletal rearrangement strategy from para-quinone methides (p-QMs) and N-fluoroarenesulfonamides is reported, enabling direct nitrogen insertion of olefins to produce a series of multiarylated (Z)-N-sulfonyl amidines with complete stereoselectivity and generally good yields. Using p-QMs without o-hydroxy substituents gave triarylated N-sulfonyl amidines, whereas tetraarylated N,N'-disulfonyl amidines were synthesized with the existence of o-hydroxy groups.

Catalytic Asymmetric Synthesis of Axially and Centrally Chiral 1,2-Dihydrobenzofuro[3,2-b]pyridines through a [2 + 2] Cycloaddition/Retroelectrocyclization/Re-Cycloaddition Cascade

A catalytic asymmetric tandem cyclization of azadienes and ortho-alkynylnaphthols accelerated by the chiral N,N'-dioxide-gadolinium(III) complex is disclosed. This method allows the synthesis of a range of 1,2-dihydrobenzofuro[3,2-b]pyridines containing both axially and centrally chiral elements in high yields and excellent stereoselectivities (up to >99% yield, 91:9 dr, 98% ee). A control experiment revealed that this process proceeded through a multistep [2 + 2] cycloaddition/retroelectrocyclization/tautomerism/1,6-conjugate addition cascade.

Copper (I) Chloride-Catalyzed Photoredox Synthesis of Multifunctionalized Compounds at Room Temperature and Their Antifungal Activities

A simple visible-light-induced CuCl-catalyzed synthesis was developed for highly functionalized carbon-centered compounds (α-alk/aryloxy-α-diaryl/alkylaryl-acetaldehydes/ketones) at room temperature using benzoquinone, alkyl/aryl alcohol, and alkyl/aryl terminal/internal alkynes. Late-stage functionalized compounds show good antifungal activities, especially against Candida krusei fungal strain, in in vitro experiments (the Broth microdilution method). Moreover, toxicity tests (zebrafish egg model experiments) indicated that these compounds had negligible cytotoxicity. The green chemistry metrics (E-factor value is 7.3) and eco-scale (eco-scale value is 58.8) evaluations show that the method is simple, mild, highly efficient, eco-friendly, and environmentally feasible.

PhIO-Mediated Oxidative C═C Bond Cleavage and Reassembly toward Highly Functionalized Oxazolones

An efficient PhIO-mediated oxidative C═C bond cleavage and reassembly of enaminone toward oxazolone with high regioselectivity has been reported. DFT calculations revealed that the reaction proceeded through an oxygen atom transfer, C═C bond cleavage, alkylthio migration, and reassembly cascade. This strategy is highlighted by high atom and step economy with formation of five bonds in one pot and generation of a high-valued oxazolone skeleton under mild conditions.

Tunable Electrocatalytic Annulations of o-Arylalkynylanilines: Green and Switchable Syntheses of Skeletally Diverse Indoles

Tunable electrocatalytic annulation reactions of o-arylalkynylanilines have been established, leading to green and divergent syntheses of skeletally diverse indoles by adjusting the electrolytes and the solvents. The presence of ammonium halides as the electrolytes enabled the halogenation of o-arylalkynylanilines to give C3-halogenated indoles whereas naphtho[1',2':4,5]furo[3,2-b]indoles could be obtained by changing the electrolyte from ammonium halides to KI. Interestingly, by combining acetone as the solvent and both NH₄I and NH₄Cl as the electrolytes, the reaction worked through an intramolecular annulation and [5 + 1] cyclization cascade to form naphtho[1',2':5,6][1,3]oxazino[3,4-a]indoles.

Visible Light-Mediated In Situ Generation of δ,δ-Disubstituted p-Quinone Methides: Construction of a Sterically Congested Quaternary Stereocenter

An unprecedented visible light-assisted and zinc triflate-catalyzed construction of a diaryl-substituted quaternary stereocenter is reported. 2-(4-Hydroxyphenyl)-substituted aldehydes and ketones have been prepared in moderate to high yields via multicomponent reaction of acetylene, benzoquinone (BQ), and indole/aniline/thiol. The reaction is believed to proceed via in situ generation of p-quinone methide through a [2+2] cycloaddition-retroelectrocyclization of BQ and acetylene in blue light followed by a zinc triflate-catalyzed vinylogous Michael addition reaction with nucleophiles.

Diastereoselective Synthesis of 1,2-Dihydrobenzofuro[3,2-b]pyridines via a Carbon-Carbon Double-Bond Cleavage/Rearrangement Cascade

A new Lewis acid-catalyzed [2 + 2] cycloaddition/retroelectrocyclization (CA-RE)/1,6-addition relay of aurone-derived 1-azadienes and 1-alkynylnaphthalen-2-ols has been reported, leading to the regio- and diastereoselective synthesis of 1,2-dihydrobenzofuro[3,2-b]pyridine with a chiral carbon center and an axial chirality in good yields. This protocol enables the C-C double-bond scission/recombination to rapidly construct aza-heterocyclic architectures and features 100% atom utilization, a wide substrate scope, good compatibility with substituents, and excellent diastereoselectivity.

Asymmetric Construction of α-Substituted β-Hydroxy Lactones via Ni Catalyzed Decarboxylative Addition Reaction

We described a Ni-bidentate oxazoline catalyzed highly enantio- and diastereoselective decarboxylative aldol reaction of 2-oxotetrahydrofuran-3-carboxylic acid/2-oxochromane-3-carboxylic acid derivatives with different kinds of carbonyls. Under optimal reaction conditions, α-substituted β-hydroxy butyrolactones and dihydrocoumarins with an all-carbon quaternary stereocenter have been generated with high levels of functional-group compatibility. Furthermore, proficient transformations of products were also described, in which an aliphatic tertiary alcohol and a multi-substituted 1,4-diol were smoothly constructed through hydrogenation and ring-opening reaction, respectively.

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.

Synthesis of C3-alkylated benzofurans via palladium-catalyzed regiocontrolled hydro-furanization of unactivated alkenes

A new chelation-controlled hydrofuranization of unactivated olefins with α-alkynyl arylols is reported for the first time, and used to produce a wide range of C₃-alkylated benzofurans with generally good yields under mild conditions.

A photoinduced arene–alkyne [3 + 2] cycloaddition cascade of 1-alkynylnaphthalen-2-ols for tunable synthesis of skeletally diverse bridged hexacycles

Photoinduced solvent-dependent cyclodimerizations of 1-alkynylnaphthalen-2-ols were developed for the first time, producing skeletally diverse bridged hexacyclic architectures with good yields and high stereoselectivities.

Synthesis of polycyclic indoles via organocatalytic bicyclization of α-alkynylnaphthalen-2-ols with nitrones

A new organocatalytic bicyclization of α-alkynylnaphthalen-2-ols with nitrones was first reported, leading to the convergent synthesis of polycyclic indoles with substantial substitution diversity in generally good yields through scission of the N-O bond of nitrones via [3,3]-sigmatropic rearrangement. This transformation showcases the use of a quinine catalyst in a complicated cascade system that has been shown to effectively construct polycyclic heterocycles via alkyne difunctionalization.

Stereoselective synthesis of fully substituted ethylenes via an Ag-catalyzed 1,6-nucleophilic addition/annulation cascade

A catalytic 1,6-nucleophilic addition/annulation cascade was developed for the first time, and used to produce 27 hitherto unreported ethylene-linked 1-naphthol-imidazole pairs with generally good yields and complete stereoselectivity. An Ag₂O-catalyzed reaction of yne-allenone esters with tosylmethyl isocyanide proceeded efficiently, and provided a simple and convergent protocol for the synthesis of fully substituted (Z)-ethylenes whereas tetrasubstituted (E)-ethylenes were obtained when ethyl isocyanoacetate was employed in this transformation. The reaction pathway consists of [2+2] cycloaddition, 1,6-nucleophilic addition and [3+2] cycloaddition, leading to continuous multiple bond-forming events including C-C and C-N bonds to construct complex molecules.

Copper-Catalyzed Annulation-Cyanotrifluoromethylation of 1,6-Enynes Toward 1-Indanones via a Radical Process

A new Cu(II)-catalyzed annulation-cyanotrifluoromethylation of 1,6-enynes with Togni's reagent and trimethylsilyl cyanide (TMSCN) has been established, enabling the direct construction of trifluoromethylated 1-indanones with an all-carbon quaternary center in good yields. This reaction was performed by using low-cost Cu(OTf)₂ as the catalyst and Togni's reagent as both the radical initiator and a CF₃ source, providing an efficient protocol for building up an 1-indanone framework with wide functional group compatibility. The reaction mechanism was proposed through a radical triggered addition/5-exo-dig cyclization/oxidation/nucleophilic cascade.

Cu(ii)-Catalyzed formal [4 + 2] cycloaddition between quinone methides (QMs) and electron-poor 3-vinylindoles

A new Cu(ii)-catalyzed formal [4 + 2] cycloaddition between quinone methides (QMs) including para-quinone methides (p-QMs) and ortho-quinone methides (o-QMs) and electron-poor 3-vinylindoles was established.

Silver-Catalyzed Nitration/Annulation of α-Alkynyl Arylols toward 3-Nitrated Benzofurans

A silver-catalyzed nitration/annulation of α-alkynyl arylols is reported by using tert-butyl nitrite (TBN) as a NO₂ radical precursor, from which a set of 3-nitrated benzofurans were synthesized with moderate to good yields. This transformation initiated by an in situ generated NO₂ radical proceeds efficiently under mild and neutral redox conditions, which provides a new pathway toward the 3-nitrobenzofuran framework via catalytic difunctionalization of internal alkynes.

I2-Promoted Multicomponent Dicyclization and Ring-Opening Sequences: Direct Synthesis of Benzo[e][1,4]diazepin-3-ones via Dual C-O Bond Cleavage

A novel and efficient formal [4 + 2+1] annulation of aryl methyl ketones and 2-aminobenzyl alcohols for the synthesis of benzo[e][1,4]diazepin-3-ones is reported. This reaction successfully affords diverse seven-membered ring lactams via dual C-O bond cleavage. A preliminary mechanistic study showed that a multicomponent dicyclization and ring-opening sequence might occur, with the introduction of methyl sulfide proposed as the last step. This efficient strategy with mild reaction conditions and a broad substrate scope has potential applications in chemistry and medicine.

Synthesis of dibenzo[a,d]cycloheptanoids via aryne insertion into 2-arylidene-1,3-indandiones

A cascade synthetic strategy for the direct synthesis of dibenzo[a,d]cycloheptanoids and dibenz[a,c]anthracene-9,14-dione derivatives from aryne precursors has been developed.

Completely regioselective insertion of unsymmetrical alkynes into electron-deficient alkenes for the synthesis of new pentacyclic indoles

A Lewis acid catalyzed insertion of unsymmetrical alkynes into electron-deficient alkenes has been reported for the first time, leading to 34 examples of hitherto unreported pentacyclic benzo[5,6]chromeno[2,3-b]indoles.