N-metalated Azomethine Ylides Research Articles

Synthesis of highly substituted spiropyrrolidines via 1,3-dipolar cycloaddition reaction of N-metalated azomethine ylides

3-Arylidene-4-chromanones undergo regioselective 1,3-dipolar cycloaddition reactions with N-metalated azomethine ylides derived from aromatic aldimines of glycine methyl ester in the presence of silver acetate and triethylamine to give spiropyrrolidine derivatives in good yield. X-Ray crystal structure analysis of one of the products confirms the structure and regiochemistry of the cycloadditions.

Stereocontrolled Synthesis of Highly Substituted Proline Esters via [3 + 2] Cycloaddition between N-Metalated Azomethine Ylides and Nitroalkenes. Origins of the Metal Effect on the Stereochemical Outcome

The [3 + 2] cycloaddition reaction between several N-metalated azomethine ylides and nitroalkenes has been studied using AgOAc and LiClO4 as metalating reagents in the presence of triethylamine. The reaction is found to be very versatile and can be extended to homochiral nitroalkenes. In general, lithium and silver salts promote preferential formation of the endo and exo cycloadducts, respectively. The presence of a phenol moiety induces a shift toward the exo-cycloadduct even when lithium is used. A model based upon the experimental results obtained and SCF-MO calculations is proposed to explain the variable stereochemical outcome of these reactions.

１，３‐双極子と金属イオンとの相互作用―１，３‐双極付加環化反応の立体・レギオ制御

This review focuses on our own attempts of metal ion-assisted stereo- and regiocontrol of 1, 3-dipolar cycloaddition reactions : N-Metalated azomethine ylides, or metal enolates, of alkylideneamino nitriles and esters undergo endo-selective cycloadditions to α, β-unsaturated carbonyl acceptors to give 1-pyrrolines and pyrrolidines. Magnesium allylic alkoxides are highly reactive in nitrile oxide cycloadditions which are exclusively syn-selective and regioselective. Equally fruitful are nitrone cycloadditions to allylic alkoxides and Lewis acidcatalyzed nitrone reactions with allylic alcohols and enones.

Diastereoselective cycloaddition of N-lithiated azomethine ylides to (E)-.alpha.,.beta.-unsaturated esters bearing a C2-symmetric imidazolidine chiral controller

The 1,3-dipolar cycloaddition of N-metalated azomethine ylides to chiral (E)-3-(1,3-disubstituted 4,5-diphenylimidazolidin-2-yl) propenoates proceeded highly diastereoselectively. The previously unknown absolute configuration of optically pure 1,2-dianilino-1,2-diphenylethane was determined from the absolute configuration of the cycloadducts. What diastereotopic olefin face of the α,β-unsaturated ester was attacked by the ylide was found to depend dramatically upon the nature of N substituents of the chiral controller as well as upon the bulkiness of the ester moiety of the ylide

Asymmetric Cycloaddition of N-Metalated Azomethine Ylides with the Optically Active α,β-Unsaturated Esters Derived from α-Amino Acids

Abstract α,β-Unsaturated esters bearing a chiral oxazolidine or perhydropyrrolo[1,2-c]imidazole auxiliary at the β-position have been prepared and applied to the cycloadditions with N-metalated azomethine ylides derived from α-(benzylideneamino) esters. These reactions are found to proceed with an exclusively high diastereofacial selectivity to give 2,4-pyrrolidinedicarboxylates with four consecutive chiral centers after the removal of chiral auxiliary. Detailed stereochemistry in the transition state is discussed.

Asymmetric 1,3-dipolar cycloadditions of azomethine ylides with a chiral electron-deficient olefinic dipolarophile

The first example of efficient asymmetric 1,3-dipolar cycloadditions of azomethine ylides is presented, where reactive N-metalated azomethine ylides and the α,β-unsaturated ester with a chiral perhydropyrrolo[1,2— c]imidazol-3-yl moiety at the β-position have been employed. The exclusive participation of thermodynamically less stable 3-H/3′-H synperiplanar conformer is based on its sterical preference in the frontier orbital- and chelation-controlled rigid wansition state.

Metallic Base-Induced Cycloadditions of N-(1-Cyanoalkyl)imines via N-Metalated Azomethine Ylides: Enhanced Reactivity and High Regio- and Stereoselectivity

Abstract Lithiation of N-(1-cyanoalkyl)imines with LDA generates new N-lithiated azomethine ylide 1,3-dipoles which show enhanced reactivity toward dipolarophiles. They undergo exclusively regio- and stereoselective 3+2 cycloaddition reaction with α,β-unsaturated esters to give 1-pyrrolines after the elimination of LiCN. Metallic bases other than LDA can be also effective. Such high regio- and stereoselectivity is explained by the involvement of N-metalated azomethine ylides.