2270-59-9

5-Bromo-2-methyl-2-pentene acts as a synthetic reagent, which is useful in the formation of sesqueterpenoid. It is also employed in the preparation of geranlol-3-14C. Further, it is used in the preparation of penifulvin A, which is a sesquiterpenoid with a novel dioxa-fenestrane structure.

1. 105 kg of THF solution of 12% methylmagnesium bromide (equivalent to 12.6 kg 100% concentration) was slowly added to a stainless steel reactor under brine bath cooling, maintaining the reaction temperature at 30-35°C. 2. 6.7 kg of cyclopropyl methyl ketone (II) was added dropwise to the reactor. 2. 6.7 kg of cyclopropyl methyl ketone (II) was added dropwise to the reactor, and after completion of the dropwise addition, the reaction mixture was stirred continuously at 30-35 °C for at least 1 hour. 3. the reaction mixture was cooled to 5-10 °C and then transferred to another enameled reactor pre-cooled to 0-10 °C containing 60 kg of 35% sulfuric acid. 4. the reaction mixture was warmed to 25-30 °C and maintained at this temperature for at least 15 minutes to ensure complete reaction. Subsequently, it was left to fully separate the two phases and remove the lower aqueous phase. 5. The organic phase was washed with 6.7 kg of softened water, stirred at 25-30 °C and left to stratify, again removing the lower aqueous phase. 6. Remove the solvent from the organic phase by vacuum distillation until an oily residue is obtained. To the residue was added 10.1 kg of THF and stirred until complete dissolution. 7. The resulting solution was transferred to a vessel of suitable capacity and prepared for the next stage of the reaction. 8. 8. 10 kg of the target product 5-bromo-2-methyl-2-pentene was finally obtained in 77% yield based on cyclopropyl methyl ketone (II).

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