Abstract
1,1-Diethoxybut-3-yn-2-one, a conjugated terminal acetylenic
ketone, reacts with nitrogen and oxygen nucleophiles and gives Michael
adducts, in most cases in good to excellent yield. In almost every
case the predominant reaction is monoaddition, which leads to formation
of the corresponding β-substituted α,β-unsaturated
ketones in a stereospecific fashion. The stereochemistry depends on
the nature of the nucleophile, the general pattern being that ammonia
and primary amines give Z -alkenones,
whereas secondary amines and alcohols afford E -alkenones.
Triethylamine does not furnish a Michael addition product, but catalyzes
a trimerization that leads to formation of a 6H -1,3-dioxine
derivative. When bis-nucleophiles, for instance hydrazine and hydroxylamine,
are used, the Michael-addition products are unstable and undergo
secondary reactions to form heterocyclic compounds, which are isolated
in excellent yields.
Key words
acetylenic ketones - Michael additions - vinyl
ketones - cyclotrimerization - acetals
