Organocatalytic Asymmetric Cyclization Reaction of 2‐Alkynyl‐3,3‐Difluoro‐3 H ‐Indoles and 2‐Mercaptoimidazoles: Access to gem ‐Difluorinated C2‐Spiro Indolines

Base-Controlled Divergent Synthesis of Fluorine-Containing Benzo[4,5]imidazo[2,1-b][1,3]thiazines from 2-Mercaptobenzimidazoles and β-CF3-1,3-Enynes

A base-controlled divergent cyclization between 2-mercaptobenzimidazoles and β-CF3-1,3-enynes providing either trifluoromethylated or fluorinated benzo[4,5]imidazo[2,1-b][1,3]thiazines has been developed. The β-CF3-1,3-enyne, as a three-carbon synthon, underwent a 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU)-catalyzed tandem hydroamination/intramolecular hydrothiolation to give CF3-substituted 3,4-dihydro-2H-benzo[4,5]imidazo[2,1-b][1,3]thiazine, whereas reaction with KOH afforded fluorinated 4H-benzo[4,5]imidazo[2,1-b][1,3]thiazine exclusively. In addition, the synthetic utility of this methodology was showcased through a variety of downstream derivatizations.

Selective Synthesis of Pyrazolonyl Spirodihydroquinolines or Pyrazolonyl Spiroindolines under Aerobic or Anaerobic Conditions

Presented herein is a condition-controlled selective synthesis of pyrazolonyl spirodihydroquinolines or pyrazolonyl spiroindolines through formal [5 + 1] or [4 + 1] spiroannulation of 2-alkenylanilines with diazopyrazolones. Mechanistically, the formation of the title products involves initial generation of a pyrazolonyl spiro-fused seven-membered ruthenacycle species serving as a key intermediate through Ru(II)-catalyzed C-H/N-H bonds metalation, carbene formation, and its migratory insertion. When the reaction is carried out under air, the key intermediate undergoes reductive elimination to afford spirodihydroquinoline. When the reaction is run under argon, the key intermediate undergoes protonation and intramolecular nucleophilic addition to furnish spiroindoline. This work provides an atom-economical protocol for the effective functionalization of alkenyl C(sp²)-H bond, allowing rapid and selective assembly of valuable spiroscaffolds with a broad range of substrates.

Stereoselective Access to Spirooxindoles and Bisoxindoles Through Organocatalyzed Asymmetric Divergent Transformations of Isatin-derived MBH Carbonates

An interesting β-isoquinidine catalyzed divergent reaction was developed to produce either spirocyclopentene oxindoles, spirocyclopentadiene oxindoles or bisoxindoles in a high enantioselective fashion. The utility of this protocol was demonstrated by the versatile transformations of the products. This work not only represents the first highly stereoselective intermolecular catalytic asymmetric allylic alkylation reaction between two isatin-derived MBH carbonate molecules but also constitutes a rare example of isatin-derived MBH carbonate-based enantioselective and α-regioselective [3+2] cycloaddition reactions.

Catalytic Enantioselective Isocyanide-Based Reactions: Beyond Passerini and Ugi Multicomponent Reactions

The development of catalytic enantioselective isocyanide-based reactions is currently of great interest because the resulting products are valuable in organic synthesis, pharmacological chemistry, and materials science. This review assembles and comprehensively summarizes the recent achievements in this rapidly growing area according to the reaction types. Special attention is paid to the advantages, limitations, possible mechanisms, and synthetic applications of each reaction. In addition, a personal outlook on the opportunities for further exploration is given at the end.

Hydroxyl group-directed, tartaric acid-catalyzed synthesis of meta-functionalized aryl ethers and phenols through domino conjugate addition/aromatization of para-quinols

A tartaric acid-catalyzed three-component reaction of para-quinols, organoboronic acids, and alcohols affords meta-alkenylated aryl alkyl ether in good yields. In the absence of alcohols, meta-functionalized phenols could be obtained selectively.

Reaction condition-dependent divergent synthesis of spirooxindoles and bisoxindoles

DABCO-catalyzed divergent transformations of isatin-derived MBH carbonates leading to either spirocyclopentene oxindoles, spirocyclopentadiene 2-oxindoles or bisoxindoles are described.

Pd-catalyzed arylation/aza-Michael addition cascade to C2-spiroindolines and azabicyclo[3.2.2]nonanones

A palladium-catalyzed arylation/aza-Michael addition cascade reaction of β-substituted cyclic enones and 2-haloanilines has been reported. Using 1 mol% Pd(PPh₃)₄ as a catalyst, C2-spiroindolines are accessed via an intermolecular vinylogous arylation of β-alkyl cyclic enones and 2-haloanilines followed by an intramolecular aza-Michael addition. The functional group tolerance of this transformation is examined by 18 examples in up to 93% yield. In the second part, we developed an α'-arylation/aza-Michael addition cascade strategy to construct azabicyclo[3.2.2]nonanones catalyzed by Pd(MeCN)₂Cl₂·PPh₃. This study provides a quick route to complex and useful spiro- and bridged-heterocycles from readily available starting materials in good yields with high regioselectivity.

Synthesis of Enantioenriched α,α-Difluoro-β-arylbutanoic Esters by Pd-Catalyzed Asymmetric Hydrogenation

Synthesis of optically active gem-difluorinated organic molecules attracts a great deal of interest due to their unique properties in pharmaceutical and agrochemical areas. Herein, a series of enantioenriched α,α-difluoro-β-arylbutanoic esters were prepared in high yields (83-99%) with moderate to excellent enantioselectivities (≤97:3 er) by palladium-catalyzed asymmetric hydrogenation.

Catalyst-free formal [4+1]/[4+2] cyclization cascade sequence of isocyanides with two molecules of acylketene formed in situ from thermal-induced Wolff rearrangement of 2-diazo-1,3-diketones

An expedient and economic approach for constructing O,O,N-spiro compounds consisting of both a 1,3-oxazine and a furan ring through a catalyst-free formal [4+1]/[4+2] cycloaddition cascade sequence of isocyanides with two molecules of acylketene formed in situ through thermal-induced Wolff rearrangement of 2-diazo-1,3-diketones was developed. The reaction displayed good functional group tolerance and was compatible with different isocyanides and 2-diazo-1,3-diketones. Furthermore, preliminary asymmetric attempts of this reaction are made by utilizing optically pure isocyanides as inputs, and moderate diastereomeric induction was observed.

Diastereoselective Synthesis of 1,3-Diyne-Tethered Trifluoromethylcyclopropanes through a Sulfur Ylide Mediated Cyclopropanation/DBU-Mediated Epimerization Sequence

A one-pot synthesis of 1,3-diyne-tethered trifluoromethylcyclopropanes starting from 2-CF₃-3,5-diyne-1-enes and sulfur ylides via a sulfur ylide mediated cyclopropanation and a DBU-mediated epimerization sequence is described in this work. This process is highly diastereoselective with broad substrate scope. Moreover, a series of synthetic transformations based on the diyne moieties were conducted smoothly, affording cyclopropanes featuring trifluoromethyl-substituted all-carbon quaternary centers.

Phosphine-catalyzed [3 + 2] cycloadditions of trifluoromethyl enynes/enediynes with allenoates: access to cyclopentenes containing a CF3-substituted quaternary carbon center

The first use of trifluoromethyl-substituted enynes/enediynes as non-classical electron-deficient olefins for phosphine-catalyzed [3 + 2] cycloaddition with allenoates is presented.

Palladium-catalyzed regioselective C–H alkynylation of indoles with haloalkynes: access to functionalized 7-alkynylindoles

A palladium-catalyzed exclusively selective alkynylation of indoles has been reported, affording concise access to 7-alkynylindoles from readily available starting materials.