Stereoselectivity of Cydoaddition of<i>N</i>-(Cyanomethyl)- and<i>N</i>-(α-Cyanobenzyl)imines with Olefinic Dipolarophiles. Synthetic Equivalents of Nitrile Ylide 1,3-Dipoles
N-(Cyanomethyl)- and N-(α-cyanobenzyl)imines derived from a variety of aldehydes and ketones can tautomerize into N-protonated azomethine ylides which undergo cycloadditions with olefinic dipolarophiles. These cycloadditions are often accompanied by the elimination of HCN, mostly in a stereospecific manner, showing these imines to be synthetic equivalents of nonstabilized nitrile ylides. Stereoselectivity
Metallic Base-Induced Cycloadditions of<i>N</i>-(1-Cyanoalkyl)imines via<i>N</i>-Metalated Azomethine Ylides: Enhanced Reactivity and High Regio- and Stereoselectivity
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.