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.
Michael Addition and Alkylation of 2-Azaallyl Anions Derived from<i>N</i>-(1-Cyanoalkyl)imines, and Stereoselective Cyclization of Imine Esters or Ketones Leading to 1-Pyrrolines
The 2-azaallyl anionsderivedfrom N-(1-cyanoalkyl)imines and DBU undergo Michael addition or alkylation to produce N-(1-alkylated 1-cyanoalkyl)imines. The Michael addition of some aryl-substituted imines are highly diastereoselective. The alkylated Michael adducts are converted into lactams through a hydrolysis and recyclization sequence. Base-induced cyclization furnishes 1-pyrrolines through a cyclization
Regio- and Enantioselective Synthesis of Novel Functionalized Pyranopyrrolidines by 1,3-Dipolar Cycloaddition of Carbohydrates
作者:George Bashiardes、Céline Cano、Bernard Mauzé
DOI:10.1055/s-2005-862385
日期:——
described for the rapid enantiomeric synthesis of a novel series of pyranopyrrolidines from readily available and inexpensive carbohydrate compounds. The major feature of the method is a highly selective [3+2] cycloadditionreaction of different azomethineylides with a chiral carbohydrate-derived enone. The reaction proved to be extremely regio- and stereoselective, giving rise to single enantiomeric