The stereochemistry and regiochemistry of the Diels–Alder reactions of 6-acetoxy-2,6-dimethyl-2,4-cyclohexadienone

Abstract

6-Acetoxy-2,6-dimethyl-2,4-cyclohexadienone (1) and maleic anhydride in boiling benzene give a single adduct, exo-5-acetoxy-l,5-dimethyl-6-oxobicyclo[2.2.2]oct-7-ene-endo-2,3-dicarboxylic acid anhydride (2). With propiolic acid 1 gives exo-5-hydroxy-l,5-dimethyl-6-oxobicyclo[2.2.2]octa-2,7-diene-2-carboxylic acid (15). The high stereoselectivity and regioselectivity of these reactions is interpretable in terms of orbital overlap, closed-shell repulsion, steric, and van der Waals – London effects.