A Synthetic Route to Chiral Tetrahydropyrroloindoles via Ring Opening of Activated Aziridines with 2-Bromoindoles Followed by Copper-Catalyzed C–N Cyclization

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.

Lewis acid-mediated synthesis of mono- and tris-indole adducts from chiral aziridines

Lewis acid-mediated regio- and stereoselective nucleophilic addition of 2- or 3-substituted indoles to non-activated aziridine-2-carboxaldehydes in dioxane afforded 2-(indol-3-ylhydroxymethyl)aziridines whose ring opening with various nucleophiles rendered multi-substituted tryptamine derivatives. The reaction of the same aziridine-2-carboxaldehyde with three moles of indole in dichloromethane yielded tris-indole adducts β-(3,3'-bisindolyl)methyl (BIM) tryptamines from sequential steps including nucleophilic addition to aldehyde, Michael type Friedel-Crafts alkylation of the mono-adduct followed by regio- and stereoselective ring-opening of the aziridine ring.

Ring-opening cyclization of activated spiro-aziridine oxindoles with heteroarenes: a facile synthetic approach to spiro-oxindole-fused pyrroloindolines

Herein, we report a facile tandem approach for the synthesis of both spiro-oxindole-fused pyrroloindolines and benzofurano-pyrrolidines via a Lewis acid-catalyzed domino ring-opening with concomitant ring annulation using activated spiro-aziridines and heteroarenes. This method offers a new class of novel spiro-fused polycyclic pyrrolidines in a one-pot and sustainable manner with good yields and high diastereoselectivity. In addition, the structure of 3d was confirmed by single X-ray crystallography analysis.

A synthetic route to 1,4-disubstituted tetrahydro-β-carbolines and tetrahydropyranoindoles via ring-opening/Pictet–Spengler reaction of aziridines and epoxides with indoles/aldehydes

A route to 1,4-disubstituted tetrahydro-β-carbolines and tetrahydropyrano[3,4-b]indoles in high yields and stereoselectivity via S_N2-type ring opening/Pictet–Spengler reaction of aziridines and epoxides with indoles is described.

Mechanistic insights into Cu-catalyzed enantioselective Friedel–Crafts reaction between indoles and 2-aryl-N-sulfonylaziridines

Computational studies were successfully carried out to provide mechanistic insights into LCu-catalyzed (L = (S)-Segphos ligand) Friedel–Crafts (F–C) reaction between indoles and 2-aryl-N-sulfonylaziridines.

Synthesis of Nonracemic 1,4-Benzoxazines via Ring Opening/Cyclization of Activated Aziridines with 2-Halophenols: Formal Synthesis of Levofloxacin

Novel 3,4-dihydro-1,4-benzoxazine derivatives have been synthesized by an efficient and simple method in excellent enantio- and diastereospecificity (ee > 99%, de > 99%). The reaction proceeds via Lewis acid-catalyzed S_N2-type ring opening of activated aziridines with 2-halophenols followed by Cu(I)-catalyzed intramolecular C-N cyclization in a stepwise fashion under one-pot conditions to furnish the 3,4-dihydro-1,4-benzoxazine derivatives in excellent yields (up to 95%). The strategy offers a short and efficient synthesis to ( S)-3-methyl-1,4-benzoxazine ( S)-3v, a late stage intermediate in the synthesis of levofloxacin.

Temperature-modulated diastereoselective transformations of 2-vinylindoles to tetrahydrocarbazoles and tetrahydrocycloheptadiindoles

The Fe(OTf)₃-catalyzed dimerization of 2-vinylindolesviadiastereoselective [4 + 2] or [4 + 3] cyclization gives rise to tetrahydrocarbazoles at low temperature or tetrahydrocycloheptadiindoles at high temperature.

Domino ring-opening cyclization (DROC) of activated aziridines and epoxides with nitrones via dual-catalysis “on water”

A simple and green approach for the synthesis of non-racemic 1,2,4-oxadiazinanes and 1,4,2-dioxazinanes with excellent yields (up to 99%) and stereoselectivity (de/ee > 99%) in water has been described.

Synthetic route to chiral indolines via Cu(OAc)2-catalyzed ring-opening/C(sp2)–H activation of activated aziridines

A novel synthetic route to functionalized indolinesviaLewis acid catalyzed ring-opening of activated aziridines followed by Cu(OAc)₂-mediated intramolecular C–H amination in one-pot with excellent enantio- and diastereospecificity (ee 99%; de >99%).