Synthesis of some medium- and large-ring cycloalk-2-ene-1,4-diones by intramolecular coupling of αω-bis-diazoketones

In the presence of Cu(acac)2(Hacac = acetylacetone) some αω-bis-diazoketones couple intramolecularly with loss of nitrogen giving cycloalk-2-ene-1,4-diones; the enediones can be converted into fused ring cyclopentenones by successive treatment with sodium dithionite and sodium hydroxide.