Alkenyl Arenes as Dipolarophiles in Catalytic Asymmetric 1,3‐Dipolar Cycloaddition Reactions of Azomethine Ylides

The use of alkenyl arenes as dipolarophiles in the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides is reported. Under appropriate reaction conditions with a Cu^I or Ag^I catalyst either the exo or the endo adduct was obtained with high stereoselectivity. This process provides efficient access to highly enantiomerically enriched 4‐aryl proline derivatives. The observed results are compatible with the blockage of one prochiral face of the 1,3‐dipole, as well as with the efficient transmission of electrophilicity towards the terminal carbon atom of the dipolarophile. This polarization results in a change from a concerted to a stepwise mechanism.     

Stereoselective Ag‐Catalyzed 1,3‐Dipolar Cycloaddition of Activated Trifluoromethyl‐Substituted Azomethine Ylides

A silver‐catalyzed 1,3‐dipolar cycloaddition of fluorinated azomethine ylides and activated olefins is reported. The reaction offers a straightforward and atom‐economical procedure for the preparation of fluorinated pyrrolidines. Broad scope and high levels of diastereoselectivity have been achieved simply by using AgOAc/PPh₃ as the catalyst system. The high efficiency of the cycloaddition relies on the presence of a metal‐coordinating group on the imine moiety, such as an ester or heteroaryl group. The asymmetric version of the cycloaddition has been developed by using Taniaphos as a chiral ligand.     

Synthesis of Spiropyrrolidines via Five‐Component 1,3‐Dipolar Cycloaddition of Azomethine Ylides and Olefinic Dipolarophiles Generated In Situ Simultaneously

An efficient and straightforward five‐component cascade protocol has been developed to synthesize the highly substituted dispiroindenoquinoxaline pyrrolidine derivatives from ninhydrin, 1,2‐phenylenediamine, sarcosine, 1,3‐indanedione, and aldehydes via cascade reactions under mild conditions, in which 1,3‐dipole azomethine ylide and the dipolarophile were simultaneously generated in situ. This novel method is complementary to the classical Huisgen cycloaddition in that it is well‐suited to the preparation of dispiroindenoquinoxaline pyrrolidine derivatives.     

Synthesis of Pyrrole‐Fused Corannulenes: 1,3‐Dipolar Cycloaddition of Azomethine Ylides to Corannulene

In the long history of corannulene chemistry, the 1,3‐dipolar cycloaddition to corannulene is unprecedented. Reported herein is the 1,3‐dipolar cycloaddition of a polycyclic aromatic azomethine ylide to corannulene, a reaction which occurs exclusively at the rim bond of corannulene, from the convex side in an exo fashion. The cycloadducts were successfully converted, by successive oxidative dehydrogenation, into pyrrole‐fused corannulenes, which exhibited pronounced solvatofluorochromism.     

1,3‐Thiazolidine‐dicarboxylates from Thioketones and Thermally Generated Azomethine Ylides

The reaction of 9H‐fluorene‐9‐thione ( 1 ) with the cis‐ and trans‐isomers of dimethyl 1‐(4‐methoxyphenyl)aziridine‐2,3‐dicarboxylate (cis‐ and trans‐ 2 , resp.) in xylene at 110° yielded exclusively the spirocyclic cycloadduct with trans‐ and cis‐configurations, respectively (trans‐ and cis‐ 3 , resp.; Scheme 1). Analogously, less‐reactive thioketones, e.g., thiobenzophenone ( 5 ), and cis‐ 2 reacted stereoselectively to give the corresponding trans‐1,3‐thiazolidine‐2,4‐dicarboxylate (e.g., trans‐ 8 ; Scheme 2). On the other hand, the reaction of 5 and trans‐ 2 proceeded in a nonstereoselective course to provide a mixture of trans‐ and cis‐substituted cycloadducts. This result can be explained by an isomerization of the intermediate azomethine ylide. Dimethyl 1,3‐thiazolidine‐2,2‐dicarboxylates 14 and 15 were formed in the thermal reaction of dimethyl aziridine‐2,2‐dicarboxylate 11 with aromatic thioketones (Scheme 3). On treatment of 14 and 15 with Raney‐Ni in refluxing EtOH, a desulfurization and ring‐contraction led to the formation of azetidine‐2,2‐dicarboxylates 17 and 18 , respectively (Scheme 4).     

Facile Method for 1,3‐Dipolar Cycloaddition Reaction of Azomethine Ylides: Highly Stereoselective Synthesis of Substituted Pyrrolidine Derivatives

The substituted pyrolidine derivatives with high stereoselectivity were obtained through cycloaddition reaction in the presence of a Lewis acid namely diethylzinc by solvent‐free grinding method.     

Intramolecular 1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Ethoxycarbonylcarbenoids and Schiff Bases

Decomposition of ethyl diazoacetate in the presence of copper, copper acetylacetonate, or copper trifluoroacetylacetonate and ethyl 4-[2-(R-imino)phenoxymethyl]-2-butenoate leads to formation of chromeno-[4,3-b]pyrrole-2,3-dicarboxylic acid derivatives. The reactions involve intermediate formation of azomethine ylides which undergo regio- and stereoselective intramolecular cycloaddition at the C=C bond to afford chromeno[4,3-b]pyrroles. The steric structure of the product depends on the configuration of intermediate ylide and nature of the substituent at the ylide nitrogen atom.     

Novel Synthesis of N‐Methyl Spiropyrrolidines by 1,3‐Dipolar Cycloaddition Reaction of Azomethine Ylides

A series of novel N‐methyl spiropyrrolidines have been synthesized in good yield by the cycloaddition reaction of azomethine ylides generated by a decarboxylative route from sarcosine and paraformaldehyde with conformationally locked s‐trans enone functionality present in the (E)‐3‐arylidene‐4‐chromanone as dipolarophiles. The structure of the title compound was established by spectroscopic techniques.     

Straightforward and Highly Diastereoselective Synthesis of a New Set of Functionalized Dispiropyrrolidines Involving Multicomponent 1,3‐Dipolar Cycloaddition with Azomethine Ylides

The diastereoselective synthesis of novel series of dispiropyrrolidines has been achieved by a one‐pot three‐component [3 + 2] cycloaddition reaction of (E)‐2‐arylideneindanones, glycine ethyl ester, and the cyclic diketones 1H‐indole‐2,3‐dione (isatin) or acenaphthenequinone. Moreover, we disclose an unprecedented epimerization of spiroadducts leading to a new family of dispiropyrrolidines with an unusual relative stereochemistry.     

Synthesis of Novel Spiro Thiazolotriazole Derivatives via 1,3‐Dipolar Cycloaddition of Azomethine Ylide

The 1,3‐dipolar cycloaddition of azomethine ylide generated in situ from isatin and sarcosine to 5‐arylmethylidene thiazolo[3,2‐b][1,2,4]triazol‐6(5H)‐ones afforded novel 1′‐methyl‐4′‐aryldispiro[indole‐3,2′‐pyrrolidine‐3′,5″‐[1,3]thiazolo[3,2‐b][1,2,4]triazole]‐2,6″ (1H)‐diones in moderate yields. The structures of all the products were characterized thoroughly by NMR, infrared spectroscopy (IR), mass spectroscopy (MS) elemental analysis together with X‐ray crystallographic analysis.