Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

The [3 + 2] cycloadditions of stabilized azomethine ylides (AMYs) derived from amino esters are well-established. However, the reactions of semi-stabilized AMYs generated from decarboxylative condensation of α-amino acids with arylaldehydes are much less explored. The [3 + 2] adducts of α-amino acids could be used for a second [3 + 2] cycloaddition as well as for other post-condensation modifications. This article highlights our recent work on the development of α-amino acid-based [3 + 2] cycloaddition reactions of N-H-type AMYs in multicomponent, one-pot, and stepwise reactions for the synthesis of diverse heterocycles related to some bioactive compounds and natural products.

One-pot double annulations to confer diastereoselective spirooxindolepyrrolothiazoles

A novel four-component reaction in one pot as an atom- and step-economic process was developed to synthesize diastereoselectively spirooxindolepyrrolothiazoles through sequential N,S-acetalation of aldehydes with cysteine and decarboxylative [3 + 2] cycloaddition with olefinic oxindoles. High synthetic efficiency, operational simplification and reaction process economy using EtOH as solvent, and only releasing CO2 and H2O as side products confer this approach favorable in green chemistry metrics analysis.

Three-Component [3+2] Cycloaddition for Regio- and Diastereoselective Synthesis of Spirooxindole-Pyrrolidines

1,3-Dipolar cycloaddition of nonstabilized azomethine ylides derived from α-C-H functionalization of tetrahydroisoquinoline for regio- and diastereoselective synthesis of spirooxindole-pyrrolidines is developed. A three-component reaction of readily available cyclic amine, aryl aldehydes, and olefinic oxindoles provides a pot, atom and step economy (PASE) approach for making spiro-heterocyclic compounds with biological interest.

Pseudo-Five-Component Reaction for Diastereoselective Synthesis of Butterfly Shaped Bispiro[Oxindole-Pyrrolidine]s

A pseudo-five-component reaction involving double decarboxylative 1,3-dipolar cycloaddition of azomethine ylides with olefinic oxindoles for the diastereoselective synthesis of bispiro[oxindole-pyrrolidine]s is developed. The major diastereomers are unique butterfly shaped compounds with a plane of symmetry. Recyclable zeolite HY acid catalyst is used to promote the reaction, and only CO₂ and H₂O are generated as byproducts.

[3 + 2] Cycloaddition and Cascade Radical Reactions for the Synthesis of Trifluoromethylated Tetrahydrobenzodiazepin-3-ones

A reaction sequence involving three-component [3 + 2] cycloaddition of azomethine ylides followed by CuI-catalyzed cascade trifluoromethyl radical addition and cyclization is developed for diastereoselective synthesis of fused-tetrahydrobenzodiazepin-3-ones.

Double 1,3-Dipolar Cycloadditions of Two Nonstabilized Azomethine Ylides for Polycyclic Pyrrolidines

Nonstabilized azomethine ylides derived from decarboxylation of oxazolidin-5-ones were used for double 1,3-dipolar cycloadditions in diastereoselective synthesis of pyrrolidine-containing tetracyclic compounds. This is the first example of one-pot and five-component reactions involving two nonstabilized azomethine ylides. Only CO₂ and water were generated as byproducts.

Stereoselective synthesis of fused tetrahydroquinazolines through one-pot double [3 + 2] dipolar cycloadditions followed by [5 + 1] annulation

The one-pot [3 + 2] cycloaddition of an azomethine ylide with a maleimide followed by another [3 + 2] cycloaddition of an azide with the second maleimide gives a 1,5-diamino intermediate which is used for a sequential aminomethylation reaction with formaldehyde through [5 + 1] annulation to afford a novel polycyclic scaffold bearing tetrahydroquinazoline, pyrrolidine, pyrrolidinedione, and N-substituted maleimide in stereoselective fashion.

Fluorous modified magnetic mesoporous silica composites-incorporated fluorous solid-phase extraction for the specific enrichment of N-linked glycans with simultaneous exclusion of proteins

Taking advantage of fluorine-fluorine interactions, fluorous solid-phase extraction (FSPE) is emerging as a novel approach in proteomics research. Notably, silica gel bound with perfluoroalkyl groups was applied to the FSPE of N-linked glycans. Based on previous studies, mesoporous silica coated magnetic nanoparticles bound with perfluoroalkyl groups were synthesized for the specific enrichment of N-linked glycans in this study. The magnetic nanoparticles-incorporated FSPE strategy successfully identified 22 N-linked glycans from the OVA digest with a concentration of 0.5μg/μL, and achieved a detection limit of 5ng/μL (with 16 N-linked glycans identified). It also showed good day-to-day reproducibility. Its selectivity towards BSA protein is 1:200 (molar ratio), showing excellent size-exclusion effect. In addition, the present method proved to be effective for the analysis of the human serum digest, opening up new prospect for the identification of glycans and proteins with other post-translational modifications in biological environment.

The copper-catalyzed asymmetric construction of a dispiropyrrolidine skeleton via 1,3-dipolar cycloaddition of azomethine ylides to α-alkylidene succinimides

N,O-Ligand/Cu(OAc)₂ catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides to α-alkylidene succinimides is developed, affording dispiropyrrolidines in excellent diastereoselectivities and enantioselectivities.

Mechanism and selectivity of N-triflylphosphoramide catalyzed (3(+) + 2) cycloaddition between hydrazones and alkenes

Brønsted acid catalyzed (3(+) + 2) cycloadditions between hydrazones and alkenes provide a general approach to pyrazolidines. The acidity of the Brønsted acid is crucial for the catalytic efficiency: the less acidic phosphoric acids are ineffective, while highly acidic chiral N-triflylphosphoramides are very efficient and can promote highly enantioselective cycloadditions. The mechanism and origins of catalytic efficiencies and selectivities of these reactions have been explored with density functional theory (M06-2X) calculations. Protonation of hydrazones by N-triflylphosphoramide produces hydrazonium-phosphoramide anion complexes. These ion-pair complexes are very reactive in (3(+) + 2) cycloadditions with alkenes, producing pyrazolidine products. Alternative 1,3-dipolar (3 + 2) cycloadditions with the analogous azomethine imines are much less favorable due to the endergonic isomerization of hydrazone to azomethine imine. With N-triflylphosphoramide catalyst, only a small distortion of the ion-pair complex is required to achieve its geometry in the (3(+) + 2) cycloaddition transition state. In contrast, the weak phosphoric acid does not protonate the hydrazone, and only a hydrogen-bonded complex is formed. Larger distortion energy is required for the hydrogen-bonded complex to achieve the "ion-pair" geometry in the cycloaddition transition state, and a significant barrier is found. On the basis of this mechanism, we have explained the origins of enantioselectivities when a chiral N-triflylphosphoramide catalyst is employed. We also report the experimental studies that extend the substrate scope of alkenes to ethyl vinyl ethers and thioethers.