[59838-04-9] · C5H8Br2 · 1,3-Dibromo-2-pentene · (MW 227.93)
(ethyl vinyl ketone equivalent used in the synthesis of sesquiterpenes)
Physical Data: bp 88 °C/3 mmHg.
Form Supplied in: colorless liquid stabilized with silver wool.
Preparative Method: is prepared in two steps from commercially available 2-pentyn-1-ol (eq 1). Reduction of the alkynic alcohol with Lithium Aluminum Hydride in the presence of Sodium Methoxide followed by bromination of the intermediate aluminate afforded the vinyl bromide which was then converted to the final product by treatment with Phosphorus(III) Bromide in pyridine.1
Handling, Storage, and Precautions: lachrymator; stored cold in an amber bottle to protect from light. Use in a fume hood.
1,3-Dibromo-2-pentene has been used as an ethyl vinyl ketone equivalent in cases where a Michael addition to the unsaturated ketone failed. b-Cyperone was synthesized using this strategy via alkylation of 6-methyl-3-butylthio-2-cyclohexen-1-one using Lithium Diisopropylamide as the base to yield the 6,6-dialkylated enone system in 60% yield (eq 2). Further elaboration resulted in the synthesis of the target sesquiterpene.1
In a related strategy, 1,3-dibromo-2-pentene was used as a building block in the synthesis of compounds related to sclerosporal (eq 3). Alkylation of (-)-carvone with the allylic bromide using Potassium t-Butoxide as base in refluxing benzene afforded two stereoisomeric products in 55% and 22% yields. These isomers could be separated by chromatography and subsequently converted to the known enones which were dehydrogenated and photochemically rearranged to guaienones.2
Ronald B. Gammill
The Upjohn Company, Kalamazoo, MI, USA