2,5-Undecanedione is a γ-diketone in which the two carbonyl groups are separated by two methylene groups.
Heinz Hunsdiecker described the synthesis of 2,5-undecanedione from 5-methylfurfural in 1942. 5-Methylfurfural 1 is first reacted with methyl propyl ketone 2 in an aldol condensation reaction to form an α,β-unsaturated carbonyl compound 3. The double bond of the side chain condensation product is reduced with sodium amalgam. The intermediate 4 is then converted to 2-methyl-5-hexylfuran 5 in a Wolff-Kishner reduction using hydrazine. An acid-catalyzed reaction at 120C cleaves the furan ring, producing 2,5-undecanedione 6.
An alternative route of synthesis starts with heptanal 1. First, the carbonyl group is protected with 1,3-propanedithiol 2, producing a dithiane 3. The dithiane is deprotonated using n-Butyllithium in tetrahydrofuran, and alkylated using 1,3-dichloro-2-butene 4 to give the intermediate 5. Hydrolysis of the dithioacetal protecting group with concentrated sulfuric acid yields 2,5-undecanedione 6, which can be worked up and purified using Girard's reagent T[1] in methanol.[2]
2,5-Undecanedione is used in the, a reaction developed by Heinz Hunsdiecker in 1942 to produce cyclopentenones from γ-ketones, in sodium hydroxide solution to produce the fragrance dihydrojasmone: