Réaction du fluoroborate de 2-benzoyl-1,2-dihydro isoquinaldonitrile avec les esters α,β-éthyléniques. II. Cas des esters oléfiniques gem-disubstitués. Stéréochimie des produits de condensation–réarrangement, dérivés du 4,5-dihydro-3H-pyrrole

The previously suggested mechanism of the condensation–rearrangement reaction of a Reissert compound hydrofluoroborate salt with reactive olefins was reexamined in the case of methyl methacrylate, itaconate, citraconate, and mesaconate. Addition of triethylamine to the reaction medium leads to the isolation of a presumed intermediate 8. Spectrometric (proton magnetic resonance) data of the compounds 8 allow us to specify their stereochemistry and in two cases to point out an isomerization equilibrium. Keywords: Reissert compound fluoroborate salt, [4 + 2] cycloaddition, stereochemistry.