1,3-DIPOLAR CYCLOADDITIONS, 102 - ISOQUINOLINIUM N-ARYLIMIDES AND ELECTRON-DEFICIENT ETHYLENE DERIVATIVES

The 1,3-cycloadditions of isoquinolinium N-phenylimide (2a) and N-(2-p yridyl)imide (2b) to twelve alpha,beta-unsaturated carboxylic esters a nd nitriles proceeded at room temp, with high yields; the reactions fu rnished tetrahydropyrazolo[5,1-alpha]isoquinoline derivatives and coul d be visually followed by the loss of the red color. In this class of azomethine imines, the imide nitrogen of 2 is the nucleophilic center which determines the regiochemistry of the additions to methyl acrylat e, acrylonitrile, and their alpha-methyl and alpha-chloro derivatives. The diastereoselectivity is low; pairs of adducts were also formed wi th dimethyl fumarate and maleate. The configurations were elucidated b y H-1 NMR analysis, which likewise provided the clue to the favored co nformation of the tricyclic system. The N-arylimides 5 do not react wi th ethylene, but the formal ethylene adducts were accessible from the cycloadducts of 5a,b to triphenylvinylphosphonium bromide by alkaline cleavage. The statistical analysis of the H-delta values of 39 cycload ducts provided a consistent set of substituent increments for the pyra zolidine protons.