Reactions of Enone Ethylene Ketals with Methyl Diazomalonate/Bis(acetylacetonato)copper(II)

Several cyclic and acyclic enones and their ethylene ketals/acetals were reacted with dimethyl diazomalonate under bis(acetylacetonato)copper(II) catalysis. Cyclohex‐2‐en‐1‐one (1) yielded only C–H insertion products 2 and 3, whereas but‐3‐en‐2‐one gave a cyclopropane albeit in very low yield. The ethylene ketals 6 of cyclopent‐2‐en‐1‐one and cyclohex‐2‐en‐1‐one gave the corresponding cyclopropanes 7, which were in turn cleaved to the ketones 8. The acetals 9 and 10 of crotonaldehyde ((E)‐but‐2‐enal) and cinnamaldehyde ((E)‐3‐phenylprop‐2‐enal), respectively, yielded C–O insertion and [2,3]‐sigmatropic rearrangement products 11b, c and 12b, c, as well as cyclopropanes 11a and 11b, all of which are polyfunctional and synthetically useful compounds.