Substitution-Controlled Selective Formation of Hexahydrobenz[ e]isoindoles and 3-Benzazepines via In(OTf)3-Catalyzed Tandem Annulations

Ring-Opening Cyclization (ROC) of spiro-Epoxyoxindoles with Indoles/Aldehydes: An Easy Access to Polyheterocyclic spiro-Oxindoles

A simple one-pot, two-step strategy for the synthesis of three-dimensional (3D) polyheterocyclic spiro-oxindoles by Lewis-acid-catalyzed Friedel-Crafts type C-3 alkylation of indoles via regioselective nucleophilic ring opening of spiro-epoxyoxindoles, followed by p-TSA-catalyzed Pictet-Spengler reaction with aldehydes in up to 98% yield and 1.4:1 diastereomeric ratio has been developed.

Magic Blue-Initiated SN2-Type Ring Opening of Activated Aziridines: Friedel-Crafts-Type Alkylation of Electron-Rich Arenes/Heteroarenes

A transition metal-free, atom-economical, and highly stereospecific synthetic approach to Friedel-Crafts-type alkylation of arenes/heteroarenes has been developed. The protocol involves the catalytic aminium radical-cation salt (Magic Blue)-initiated SN2-type nucleophilic ring opening of activated aziridines with arenes/heteroarenes to give the corresponding 2,2-diarylethylamines up to 99% yield and 85% ee (for nonracemic aziridines) in a very short reaction time. Moreover, on reaction with 1,3-dimethylindole and benzofuran, aziridines undergo domino-ring-opening cyclization (DROC) to give the various biologically significant heterocyclic scaffolds in moderate to good yields.

Rapid Synthesis of 3-Methyleneisoindolin-1-ones via Metal-Free Tandem Reactions of Ester-Functionalized Aziridines

We have disclosed a novel metal-free tandem cyclization reaction for the synthesis of 3-methyleneisoindolin-1-ones starting from ester-functionalized aziridines. This strategy can be effectively promoted by DBU and carboxylic acids. Mechanistically, it involves sequential ring opening of aziridines with carboxylic acids, lactamization, and elimination of carboxylic acids.

Catalytic Aminium Radical-Cation Salt (Magic Blue)-Initiated SN2-Type Nucleophilic Ring-Opening Transformations of Aziridines

A simple and atom economic protocol for the construction of C-X/C-C bonds via catalytic aminium radical-cation salt (Magic Blue)-initiated SN2-type nucleophilic ring-opening transformations of racemic and nonracemic aziridines with different hetero and carbon nucleophiles to afford various amino ethers, thioethers, and amines in up to 99% yield, and with perfect enantiospecificity for some substrates but reduced ee with others (for nonracemic aziridines), is developed. This aminium radical-cation salt-initiated, SN2-type nucleophilic ring-opening strategy, along with various cyclization protocols, is employed to synthesize various biologically significant compounds.

Route to Functionalized Tetrahydrobenzo[d]azepines via Re2O7-Mediated Intramolecular Friedel-Crafts Reaction

We describe a Re2O7-mediated intramolecular dehydrative Friedel-Crafts reaction for the efficient synthesis of various benzo-fused heterocycles such as benzazepines and benzazocines. This process is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. The potential application of this methodology was exemplified by the facile preparation of a NMDA antagonist as well as a key intermediate en route to SKF 38393.

Ring-Opening Cyclization (ROC) of Aziridines with Propargyl Alcohols: Synthesis of 3,4-Dihydro-2H-1,4-oxazines

Activated aziridines react with propargyl alcohols in the presence of Zn(OTf)₂ as the Lewis acid catalyst following an S_N2-type ring-opening mechanism to furnish the corresponding amino ether derivatives. Those amino ethers further undergo intramolecular hydroamination via 6-exo-dig cyclization in the presence of Zn(OTf)₂ as the catalyst and tetrabutylammonium triflate salt as an additive under one-pot two-step reaction conditions. However, for nonracemic examples, ring-opening and cyclization steps were conducted under two-pot conditions. The reaction works well without any additional solvents. The final 3,4-dihydro-2H-1,4-oxazine products were obtained with 13 to 84% yield and 78 to 98% enantiomeric excess (for nonracemic examples).

Stereoselective Routes to Hexahydropyrroloindoles and Tetrahydropyrroloquinolines from Activated Aziridines and Electron Deficient 3H-Indoles

An unprecedented and novel synthetic route to hexahydropyrrolo[2,3-b]indoles bearing cis-contiguous stereocenters with excellent stereoselectivities (ee of >99%, dr of ≤99:1) has been disclosed that proceeds through the ring opening of activated aziridines with electron deficient 4-substituted indoles followed by a novel cyclization in a domino fashion, thereby obviating the use of 3-substituted indoles as the prerequisite nucleophile. Another efficient synthetic route to tetrahydropyrrolo[4,3,2-de]quinolines in excellent yields (≤93%) and excellent enantioselectivity (ee of >99%) has been established via ring opening of activated aziridines with 4-bromo-1-methyl-1H-indole at relatively higher temperatures followed by Cu(I)-catalyzed intramolecular C-N cyclization in the same pot. The stability and the formation of products at different temperatures are explained by computational studies.

Synthesis of Chiral Tetrahydro-3-benzazepine Motifs by Iridium-Catalyzed Asymmetric Hydrogenation of Cyclic Ene-carbamates

A highly efficient N,P-ligated iridium complex is presented for the simple preparation of chiral tetrahydro-3-benzazepine motifs by catalytic asymmetric hydrogenation. Substrates bearing both 1-aryl and 1-alkyl substituents were smoothly converted to the corresponding hydrogenated product with excellent enantioselectivity (91-99% ee) and in isolated yield (92-99%). The synthetic value of this transformation was demonstrated by a gram-scale hydrogenation and application in the syntheses of trepipam and fenoldopam.

Synthesis of chiral β-substituted γ-amino-butyric acid derivatives via enantioconvergent ring opening of racemic 2-(hetero)aryl aziridines with ketene silyl acetals

Lewis acid-catalyzed enantioconvergent ring opening of racemic 2-(hetero)aryl-N-sulfonyl aziridines with ketene silyl acetals is developed.

Construction of 4-spiroannulated tetrahydroisoquinoline skeletons via a sequential ring opening of aziridines and Pictet–Spengler reaction

A stepwise cyclization involving sequential ring opening of aziridines and Pictet–Spengler reaction has been developed for the synthesis of 4-spiroannulated tetrahydroisoquinoline compounds (22 examples).

Ammonium Salt-Catalyzed Ring-Opening of Aryl-Aziridines with β-Keto Esters

We herein report an ammonium salt-catalyzed protocol for the regioselective ring opening of aryl-aziridines with β-keto esters. The reaction gives access to a variety of highly functionalized target molecules with two consecutive stereo-genic centers and can be rendered enantioselective (up to e.r. = 91:9) by using bifunctional chiral ammonium salt catalysts.

Highly Selective Synthesis of Tetrahydronaphthaleno[60]fullerenes via Fullerene-Cation-Mediated Intramolecular Cyclization

A high-yielding protocol to construct six-membered carbon rings on fullerene is presented. This methodology with in situ fullerene-cation-mediated intramolecular cyclization provides high selectivity and efficient access to six-membered tetrahydronaphthaleno[60]fullerenes with a remarkable functional group tolerance and excellent yields. Furthermore, high solubilities of tetrahydronaphthaleno[60]fullerenes are reported.

Survey of natural products reported by Asian research groups in 2018

The new natural products reported in 2018 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2018 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

The one pot asymmetric synthesis of 3,3'-pyrrolidonyl spiroxindoles via a regio- and stereoselective domino reaction

A highly efficient regio- and stereoselective domino aziridine ring opening and lactamization reaction between aziridines and 3-carboxy oxindole esters has been developed for the one pot asymmetric synthesis of 4-aryl-3,3'-spiropyrrolidonyl oxindoles with excellent selectivity (dr >99 : 1 and ee up to >99%). It was further extended to a sequential one pot protocol for the asymmetric synthesis of NH-free 3,3'-pyrrolidonyl spiroxindole, maintaining the same selectivity.

Diastereoselective Construction of 2-Aminoindanones via an In(OTf)3-Catalyzed Domino Reaction

An In(OTf)₃-catalyzed domino reaction involving sequential oxidative ring opening of aziridines by using the solvent dimethyl sulfoxide and intramolecular Michael addition has been developed for the modular synthesis of 2-aminoindanone compounds by the formation of one new C═O bond and one new C-C bond. The notable feature of this strategy includes broad substrate scope, excellent trans-diastereoselectivities, highly functionalized products, and mild conditions. The catalyst In(OTf)₃ plays an important role in the formation of the indanone ring.