Stereospecificity of a New Reaction of L-Ascorbic Acid with Cis and Trans Olefinic 1,4-Dicarbonyl Compounds

The Michael-type addition of the ascorbate carbanion upon α,β-unsaturated carbonyl compounds is compared with the aldol-like addition of the same carbanion to the related 1,4-dioxo olefins. In contrast to the behavior of maleic aldehyde and 3-acetylacrolein that leads to 4, the primary aldol adduct of 1 to fumaric aldehyde is stabilized by internal Michael addition as a tetracyclic lactone–cycloketal hemiacetal (6). This structure is based on ¹³C NMR, ¹H NMR, and ultimately X-ray crystallographic work.