Lewis acid-catalyzed formal [3+2] cycloadditions of N-tosyl aziridines with electron-rich alkenes via selective carbon-carbon bond cleavage

Vinylogous and stereoselective domino synthesis of pyrano[2,3-c]pyrroles from alkylidene meldrum's acids

A domino Vinylogous aza-Michael-Aldol-Cyclocondensation (aza-VMAC) reaction was achieved with a series of alkylidene Meldrum's acid derivatives under simple operational conditions paving the way to novel pyrano[2,3-c]pyrroles in an excellent diasteroselectivity (>96 : 4), encompassing the relative control of three contiguous stereocenters.

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

NHC-catalyzed [4 + 2] annulations of allenoates and 2,3-dioxopyrrolidine derivatives

A facile NHC-catalyzed [2 + 4] annulation of allenoates with 2,3-dioxypyrrolidine derivatives was discovered, which paved a new avenue for the construction of highly substituted pyranopyrrole with moderate to good yields, high atom economy and mild reaction conditions.

Synthesis of polycyclic spiroindolines via the cascade reaction of 3-(2-isocyanoethyl)indoles

Tandem reactions of the yttrium(iii) catalyzed ring-opening reaction of 2,2'-diester aziridines with 3-(2-isocyanoethyl)indoles and the subsequent Friedel-Crafts/Mannich/desulfonylation were reported. A series of polycyclic spiroindolines containing tetrahydro-β-carbolines were obtained in moderate to excellent yields (56-92%) in one step under mild reaction conditions. A possible catalytic mechanism was also proposed.

Catalytic Asymmetric Hydroacyloxylation/Ring-Opening Reaction of Ynamides, Acids, and Aziridines

A highly enantioselective three-component reaction of ynamides with carboxylic acids and 2,2'-diester aziridines has been realized by using a chiral N,N'-dioxide/Ho(OTf)₃ complex as a Lewis acid catalyst. The process includes the formation of an α-acyloxyenamide intermediate through the addition of carboxylic acids to ynamides and the following enantioselective nucleophilic addition to in-situ-generated azomethine ylides induced by the chiral catalyst. A range of amino acyloxyenamides are delivered in moderate to good yields with good ee values. In addition, a possible catalytic cycle with a transition model is proposed to elucidate the reaction mechanism.

Asymmetric cycloisomerization/[3 + 2] cycloaddition for the synthesis of chiral spiroisobenzofuran-1,3′-pyrrolidine derivatives

An asymmetric tandem cycloisomerization/[3 + 2] cycloaddition reaction of 2,2′-diester aziridine and 2-ethynyl benzyl alcohol with Au(i)/chiral N,N′-dioxide−Dy(iii) as a relay catalyst system was developed.

Aziridine used as a vinylidene unit in palladium-catalyzed [2 + 2 + 1] domino annulation

A series of chromone fused methylenecyclopentanes are efficiently constructed in moderate to good yields by Pd-catalyzed [2 + 2 + 1] annulation, in which aziridine is used as a vinylidene unit by cleavage of two C–N bonds for the first time.

Sc(OTf)3 catalyzed [3 + 2]-annulation reaction of donor–acceptor aziridines with methylene exo-glycals: synthesis of chiral carbohydrate-spiro-heterocycles

A Sc(OTf)₃ catalyzed [3 + 2]-annulation reaction between D–A N-tosyl aziridines and methylene exo-glycals was developed for the synthesis of carbohydrate-spiro-heterocycles.

Synthesis of Structurally Diverse 3-, 4-, 5-, and 6-Membered Heterocycles from Diisopropyl Iminomalonates and Soft C-Nucleophiles

Herein, we present a general synthetic strategy for the preparation of 3-, 4-, 5-, and 6-membered heterocyclic unnatural amino acid derivatives by exploiting facile Mannich-type reactions between readily available N-alkyl- and N-aryl-substituted diisopropyl iminomalonates and a wide range of soft anionic C-nucleophiles without using any catalyst or additive. Fully substituted aziridines were obtained in a single step when enolates of α-bromo esters were employed as nucleophiles. Enantiomerically enriched azetidines, γ-lactones, and tetrahydroquinolines were obtained via a two-step catalytic asymmetric reduction and cyclization sequence from ketone enolate-derived adducts. Finally, highly substituted γ-lactams were prepared in one pot from adducts obtained using acetonitrile-derived carbanions. Overall, this work clearly demonstrates the utility of iminomalonates as highly versatile building blocks for the practical and scalable synthesis of structurally diverse heterocycles.

Accessing polysubstituted oxazolidines, pyrrolidines and imidazolidines by regioselective [3 + 2] annulations of ketenimines with donor–acceptor oxiranes and aziridines

Diverse five-membered rings result from formal [3 + 2] cycloadditions of ketenimines with carbonyl and azomethine ylides.

Construction of thiazines and oxathianes via [3 + 3] annulation of N-tosylaziridinedicarboxylates and oxiranes with 1,4-dithiane-2,5-diol: application towards the synthesis of bioactive molecules

Efficient construction of functionalized thiazine and oxathiane derivatives via [3 + 3] annulation of N-tosylaziridinedicarboxylates and oxiranes with in situ generated mercaptoaldehyde in the presence of a Lewis acid is described.

Enantioselective [3+2] cycloaddition of azomethine ylides and aldehydes via Ni/bis(oxazoline)-catalyzed ring opening of N-tosylaziridines through a chirality transfer approach

An enantioselective [3+2] cycloaddition of N-tosylaziridines and aldehydes catalyzed by a Ni(ii)-bisoxazoline complex has been accomplished through a chirality transfer approach.

Asymmetric [3 + 2] cycloaddition of donor-acceptor aziridines with aldehydes via carbon-carbon bond cleavage

An enantioselective [3 + 2] annulation of donor-acceptor aziridines with aldehydes has been realized using a Nd(OTf)3/N,N'-dioxide/LiNTf2 catalyst system, providing various chiral cis-1,3-oxazolidines in moderate to good yields with high levels of stereocontrol. A relay catalytic process is proposed where LiNTf2 promotes the formation of azomethine ylide intermediates, and a chiral Nd(iii)-N,N'-dioxide complex accelerates the asymmetric cycloaddition.

A Simple, Effective, Green Method for the Regioselective 3-Acylation of Unprotected Indoles

A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)₃ in catalytic amounts is found to be the best catalyst together with the commercially available ionic liquid [BMI]BF₄ (1-butyl-3-methylimidazolium tetrafluoro-borate) as solvent. The reaction is completed in a very short time using monomode microwave irradiation. The catalyst can be reused up to four times without significant loss of activity. A range of substituted indoles are investigated as substrates, and thirteen new compounds have been synthesized.

An unprecedented ring-opening reaction of N-(aziridin-2-ylmethylene)hydrazines to facile synthesis of functionalized enamines catalysed by Lewis acid

An interesting Lewis acid-catalysed ring-opening reaction of N-(aziridin-2-ylmethylene)hydrazines has been described in this context. A variety of functionalized enamines could be obtained in good yields through a highly regioselective cleavage of a carbon-nitrogen single bond in the aziridines along with a 1,2-migration of the substituent.

Lewis acid-catalyzed [3 + 2]cyclo-addition of alkynes with N-tosyl-aziridines via carbon-carbon bond cleavage: synthesis of highly substituted 3-pyrrolines

A novel, efficient, and highly regioselective Lewis acid-catalyzed [3 + 2] cycloaddition of alkynes with azomethine ylides, which are easily obtained from N-tosylaziridines via C-C bond heterolysis at room temperature was developed. Moderate enantioselectivity (70% ee) can be achieved by the application of the commercially available chiral Pybox 7 as the ligand.

Nickel(II)-catalyzed diastereoselective [3+2] cycloaddition of N-tosyl-aziridines and aldehydes via selective carbon-carbon bond cleavage

An efficient and mild Ni(ClO(4))(2)-catalyzed [3+2] cycloaddition of N-tosylaziridines and aldehydes via C-C bond cleavage was developed. The cycloaddition reaction proceeds with high diastereoselectivity and regioselectivity leading to highly substituted 1,3-oxazolidines. Notably, this novel reaction can be easily expanded to gram level scale and the thermal conditions cannot achieve the same transformation.