From Ring-Expansion to Ring-Contraction: Synthesis of γ-Lactones from Cyclobutanols and Relative Stability of Five- and Six-Membered Endoperoxides toward Organic Bases

Cyclobutanols undergo ring expansion with molecular oxygen in the presence of Co(acac)(2) to afford 1,2-dioxarie-hemiperoxyketals. In the course of acylation, we observed that endoperoxides rear-ranged into gamma-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.