endo/exo Facial selectivities in cycloaddition reactions of substituted 1,2,3-triazolium-1-methanides, unstabilised 1,3-dipoles, with some alkene dipolarophiles: models for 1,2,3-triazolium-1-aminides: new tetracyclic pyrrolo[1,2-c][1,2,3]benzotriazole structures: azolium 1,3-dipoles

Abstract

endo/exo Stereochemistry in the cycloaddition reactions of substituted 1,2,3-triazolium-1-aminide and 1,2,3-triazolium-1-methanide 1,3-dipoles has been explored for the dipolarophiles acrylonitrile and N-substituted maleimides. The cycloadditions with acrylonitrile displayed predominant endo-geometry but gave mixtures of endo- and exo-isomers. In contrast N-substituted maleimides gave almost exclusive exo-cycloadducts. The cycloaddition products are novel tri- and tetracyclic structures. Factors affecting endo/exo selectivities are discussed for these systems. Generalisations are not reliable and each 1,3-dipole–dipolarophile pair needs to be carefully considered.