Catalytic Double [2 + 2] Cycloaddition Relay Enabled C-C Triple Bond Cleavage of Yne-Allenones

Lewis Acid-Catalyzed Remote Site-Selective Ring Deconstruction of Cyclobuteno[a]naphthalene-4-ones to Access Unsymmetric 1,1-Diarylated Olefins

A catalytic site-selective ring deconstruction of cyclobuteno[a]naphthalene-4-ones with alcohols is reported, enabling the direct production of a wide range of unsymmetric 1,1-diarylated olefins with good yields and complete regioselectivity. The late-stage application of these resulting terminal olefins demonstrates great possibilities to apply this strategy to complex molecules. The protocol features good functional group compatibility, broad substrate scope, and controllable site selectivity.

Enantio- and Regioselective CuH-Catalyzed Conjugate Reduction of Yne-Allenones

A new asymmetric catalytic conjugate reduction of yne-allenones to synthesize enantioenriched cyclobuta[a]naphthalen-4(2H)-ones has been established that uses copper-bisphosphine complexes as catalysts and gives excellent regio- and enantioselectivities (≥99% ee) in most cases. This protocol tolerates a broad scope of substrates, exhibits high compatibility with various substituents, and gives excellent stereoselectivity, providing a catalytic and efficient entry to fabrication of synthetically important chiral 6-6-4 tricarbocyclic scaffolds.

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.

Iron-catalyzed hydrogen atom transfer induced cyclization of 1,6-enynes for the synthesis of ketoximes: a combined experimental and computational study

An iron-catalyzed reductive radical cyclization/hydro-oximation of 1,6-enynes with tBuONO was developed, leading to functionalized benzofuran, benzothiophene, and cyclopentenyl-based ketoximes.

Transition metal-free cyclobutene rearrangement in fused naphthalen-1-ones: controlled access to functionalized quinones

The divergent preparation of 1,4-naphthoquinones and tetraphene-7,12-diones, which bear the ABCD-ring of landomycins, has been accomplished directly through oxidative reorganization of previously non-isolable cyclobuta[a]naphthalen-4(2H)-ones.

Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as “O” source and for the regeneration of the photocatalyst.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature.

Photoinduced double [2 + 2] cycloaddition relay of yne–allenones for highly diastereoselective synthesis of hexacyclic 1-naphthols

A new photoinduced photocatalyst-free energy-transfer strategy for double [2 + 2] cycloaddition relay of yne–allenones is reported for the first time and used to produce a series of hitherto unreported hexacyclic 1-naphthols.

NaOH-Promoted Chemoselective Cascade Cyclization of Cyclopropyl Esters with Unsaturated Imines: Access to Bioactive Cyclopenta[c]pyridine Derivatives

A chemoselective cascade cycloaddition reaction is developed for green and efficient access to cyclopenta[c]pyridine derivatives. Simple and inexpensive NaOH is used as the sole catalyst for this process. The δ-carbon of cyclopropyl ester is activated as a nucleophilic carbon to initiate highly chemoselective cascade reactions. Cyclopenta[c]pyridines bearing various substituents are afforded in excellent yields. Preliminary studies on the bioactivities of the afforded products show promising antibacterial activities for potential applications in plant protections.

Direct Transformation of Terminal Alkynes into Amidines by a Silver-Catalyzed Four-Component Reaction

An unprecedented conversion of terminal alkynes into N-sulfonimidamides (amidines) is reported by a silver-catalyzed, one-pot, four-component reaction with TMSN₃, sodium sulfinate, and sulfonyl azide. The reaction scope includes both aromatic and aliphatic alkynes. A possible cascade reaction mechanism, consisting of alkyne hydroazidation, sulfonyl radical addition, 1,3-dipolar cycloaddition by TMSN₃, and retro-1,3-dipolar cycloaddition, is proposed. TMSN₃ is found to play an essential role in each step of the reaction.

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.

A bicyclization reaction with two molecular allenyl ketones and isocyanides: synthesis of a lactone-containing azaspirocycle derivative

A novel bicyclization reaction of two molecular allenyl ketones and isocyanides has been disclosed. This strategy allows for the construction of structurally complex spirocyclic lactam–lactone systems in an efficient manner.

Phosphine-mediated sequential annulations of allenyl ketone and isocyanide: a bicyclization strategy to access a furan-fused eight-membered ring and a spirocycle

Phosphine-mediated cascade annulations of allenyl ketone and isocyanide have been disclosed. This strategy enables the efficient synthesis of a furan-fused eight-membered ring and a spirocycle.

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.

Iron-catalyzed reductive cyclization reaction of 1,6-enynes for the synthesis of 3-acylbenzofurans and thiophenes

A facile synthesis of 3-acylbenzofurans and thiophenes via iron(ii)-catalyzed reductive cyclization of 1,6-enynes has been developed.

Fe(III)-Catalyzed Bicyclization of Yne-Allenones With Indoles for the Atom-Economic Synthesis of 3-Indolyl Cyclobutarenes

A new Fe(III)-catalyzed bicyclization reaction of yne-allenones with indoles has been established, enabling the direct construction of cyclobuta[a]naphthalen-4-ols with an all-carbon quaternary center in good to excellent yields. This reaction was performed by using low-cost FeCl3 as the catalyst and EtOH as the environmentally benign solvent, providing a green protocol for constructing the cyclobutarene framework with a high degree of atom economy and functional group compatibility. The reaction mechanism was proposed to proceed through a [2 + 2] cycloaddition/1,6-conjugate addition cascade.

Atom-economic synthesis of cyclobuta[a]naphthalen-4-ols via a base-promoted [2 + 2] cycloaddition/1,6-nucleophilic addition cascade

A first atom-economic [2 + 2] cycloaddition/1,6-conjugate addition cascade of yne-allenones with C-nucleophiles including 1,3-dicarbonyls and α,α-dicyanoolefins under base-promoted conditions has been established, enabling the direct construction of C(sp3)-C(sp3) bonds to generate cyclobuta[a]naphthalen-1-ols with generally good yields. These resulting products have a cyclobutene unit that contains both an aryl and alkyl group.