Competing formations of oxonium and carbonyl ylides with carbonylcarbenes

A series of 2-mono- and 2,2-disubstituted 1,3-dioxepin derivatives, two of which also had a carbonyl function in one of their 2-R groups, were prepared and reacted with dimethyl diazomalonate with copper(II) acetylacetonate as a catalyst. Ylide formation probabilities with allyl ether and/or carbonyl functions were investigated. A chemoselectivity in favor of carbonyl ylide was observed.