Oxidation of ketones by ferric perchlorate in the presence of conjugated dienes to hexahydrofuro[2,3-b]furans and 1,6-dioxaspiro[4,4]nonanes

Iron(III) perchlorate nonahydrate (FEP) in acetonitrile in the presence of conjugated dienes oxidizes carbonyl compounds (aldehydes and ketones) to α,α-diaddition products hexahydrofuro[2.3-b]-furans 3, in moderate yield (nine examples). α,α-Disubstituted ketones afford the α,α′-diaddition products 1,6-dioxaspiro[4,4]nonanes 4 or monoaddition products 6 and 7. The isomer distribution and the influence of the reaction conditions are discussed based on selective oxidative deprotonation of the carbonyl compound by iron(III) and addition of α-carbonylalkyl radicals to conjugated olefins