The Lewis acid-catalyzed [3+1+1] cycloaddition of azomethine ylides with isocyanides

Chiral phosphoric acid-catalyzed enantioselective [5+1] cycloaddition reaction of C,N-cyclic azomethine imines with isocyanides

The first catalytic enantioselective [5+1] cycloaddition reactions of C,N-cyclic azomethine imines with isocyanides are reported herein. The method displays a broad substrate scope and atom-economy. A series of chiral tetrahydroisoquinoline containing indole skeletons were obtained in up to 90% yield with 95% ee under mild reaction conditions. A possible catalytic model was also proposed.

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.

Enantioselective Synthesis of Azetidines through [3 + 1]-Cycloaddition of Donor-Acceptor Aziridines with Isocyanides

The enantioselective [3 + 1]-cycloaddition of racemic donor-acceptor (D-A) aziridines with isocyanides was first realized under mild reaction conditions using a chiral N,N'-dioxide/Mg^II complex as catalyst, providing a facile route to enantioenriched exo-imido azetidines with good to excellent yield (up to 99%) and enantioselectivity (up to 94% ee). An obvious chiral amplification effect was observed in this system, and an explanation was elucidated based on the experimental investigation and X-ray crystal structure of the enantiomerically pure catalyst.

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.

Synthesis of strained 1,2-diazetidines via [3 + 1] cycloaddition of C,N-cyclic azomethine imines with isocyanides and synthetic derivation

Strained diazetidines are assembled simply from 1,3-dipolar cycloaddition of isocyanides and C,N-cyclic azomethine imines, and their diversified transformations are presented.

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.

Asymmetric synthesis of tetrazole and dihydroisoquinoline derivatives by isocyanide-based multicomponent reactions

Although isocyanide-based multicomponent reactions were proven to be simple, elegant and facile strategies for the synthesis of highly valuable nitrogen-containing heterocycles, their asymmetric versions accessing to optically active nitrogen heterocyclic compounds are rather limited. Here, we illustrate that, relying on the enantioselective addition of simple isocyanides to C=C bonds, several isocyanide-based multicomponent reactions are realized in the presence of a chiral MgII-N,N'-dioxide catalyst. In the reaction among isocyanide, TMSN3, and alkylidene malonate, three- or four-component reactions could be precisely controlled by modulating reaction conditions, supplying two types of enantioenriched tetrazole-derivatives in moderate to high yields. Possible catalytic cycles via a key zwitterionic intermediate, and the vital roles of H2O or excess ligand are provided based on control experiments. Moreover, taking advantage of this zwitterionic intermediate as a 1,3-dipole, an enantioselective dearomative [3+2] annulation reaction of nonactivated isoquinolines is achieved, furnishing chiral 1,2-dihydroisoquinolines in good to excellent results.

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

This review covers the use of 2-azaallyl anions, 2-azaallyl cations, and 2-azaallyl radicals in organic synthesis up through June 2018. Particular attention is paid to both foundational studies and recent advances over the past decade involving semistabilized and nonstabilized 2-azaallyl anions as key intermediates in various carbon-carbon and carbon-heteroatom bond-forming processes. Both transition-metal-catalyzed and transition-metal-free transformations are covered. Azomethine ylides, which have received significant attention elsewhere, are discussed briefly with the primary focus on critical comparisons with 2-azaallyl anions in regard to generation and use.

Recent advances in synthetic facets of immensely reactive azetidines

Recent developments in synthetic strategies towards functionalized azetidines along with their versatility as heterocyclic synthons.

Efficient Synthesis of Fully Substituted Pyrrolidine-Fused 3-Spirooxindoles via 1,3-Dipolar Cycloaddition of Aziridine and 3-Ylideneoxindole

Drug-like spirocyclic scaffolds have been prepared by fusing fully functionalized pyrrolidine with oxindoles in an approach based on 1,3-dipolar cycloaddition. Reaction between aziridine and 3-ylideneoxindole generated diverse spirooxindole-pyrrolidines in good yield (up to 95%) with high diastereoselectivity (up to >20:1). The reaction also proceeded smoothly with several other synthetically useful activated trisubstituted olefins. The mild reaction conditions, short reaction times, and high tolerance for various substitutions make this approach attractive for constructing pharmacologically interesting spiro-architectures.

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.

Isocyanide-based multicomponent reactions in the synthesis of heterocycles

In this review, we update our previous presentation, underscoring the recent applications of isocyanides as privileged synthons in the synthesis of various heterocyclic compounds, especially focused on those synthesizedviamulticomponent reactions.

Phosphinic acid-promoted addition reaction of isocyanides to (Z)-hydroximoyl chlorides: efficient synthesis of α-(hydroxyimino)amides

The reaction of (Z)-hydroximoyl chlorides with isocyanides promoted by phosphinic acid in the presence of triethylamine proceeds smoothly to afford α-(hydroxyimino)amides in good to high yields.