Bromo-3-methyl-2-butene

One hundred grams (1.46 moles) of freshly distilled isoprene (b.p. 33.5-34.5°) is cooled in an ice-salt mixture, and a solution of 122 g. (1.52 moles) of hydrogen bromide in 285 g. of acetic acid is added. The mixture is allowed to stand in the refrigerator for 2 days, after which it is poured into 2 1. of ice water. The dark oil is separated, dried over calcium chloride, and distilled under reduced pressure. There is obtained 163 g. (74%) of l-bromo-3-methyl-2-butene boiling at 26-33°/12 mm. 

---

To a stirred solution of 500 mg (1.4 mmol) of 4 in 10 mL of THF at —100 °C is added 1.4 mmol (1 M THF soln) of NaHMDS dropwise. The mixture is stirred for 30 min at —100°C and 500 pi (4.3 mmol, 3 equiv) of 1-bromo-3-methyl-2-butene is added. After stirring for an additional 40 min at —100 the mixture is poured into H20 and extracted with EtOAc. The combined organic extracts are dried over Na3S04 and concentrated, Chromatography (silica gel, CH2C12) gives 6 [R = (CH3)2C = CHCH2] yield 405 mg (68%). 

C5H9Br 1 -bromo-3-methyl-2-butene 870-63-3 384.00 33.720 2 5076 C5H9CI02 butyl chloroformate 592-34-7 415.15 35.795 1,2... 

How would you synthesize Pentazocine from 1 -bromo-3 -methyl-2-butene Explain the route of synthesis. 

Obtained by reaction of 1-bromo-3-methyl-2-butene with phloropro-piophenone in the presence of the weakly basic resin DeAcidite H-IP (OH" form) in boiling benzene for 16 h (12%) [7739]. The yield was similar to the one obtained by using 2-methyl-3-buten-2-ol and a Lewis acid but the isolation was simpler. 

Reaction between phioracyiphenone and 1-bromo-3-methyl-2-butene in the presence of the weak basic ion exchange resin DeAcidite H-IP (in the OH-form). The yields vary between 10% and 15% (98). 

---