Abstract
Cyclobutanols undergo ring expansion with molecular oxygen in the presence of Co(acac)2 to afford 1,2-dioxane-hemiperoxyketals. In the course of acylation, we observed that
endoperoxides rearranged into γ-lactone in the presence of triethylamine. Thus, a
generalization of this ring contraction through a Kornblum–DeLaMare rearrangement
is here reported. Application of this transformation to monosubstituted 1,2-dioxane
derivatives also led to 1,4-ketoaldehydes, in proportions depending on the nature
of the substituent. These same conditions applied to five-membered dioxolane analogues
led to fragmentation instead, through a retro-aldol type process. This study emphasizes
the difference of stability of 1,2-dioxane and 1,2-dioxolane against organic bases,
1,2-dioxolanes having proved to be particularly reactive whereas 1,2-dioxanes showed
a relative tolerance under these conditions.
Key words peroxides - ring contraction - ring-expansion - lactones - fragmentations - rearrangement
- heterocycles
