Eistert's Methyl Enol Ethers of Acetylacetone

Abstract

The configuration and conformation of the two isomeric methyl enol ethers of acetylacetone (1) have been unequivocally demonstrated. The n.m.r. solvent shift data and observation of nuclear Overhauser effects support an s-cis conformation for the more stable isomer 2 bearing acetyl trans to methoxyl while indicating an s-trans conformation for the less stable enol ether 3 having acetyl cis to methoxyl. The facile acid-catalyzed isomerization of 3 to 2 apparently proceeds by reversible protonation of carbonyl oxygen since no deuterium incorporation is observed when the isomerization is performed in acetic acid-d4.