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 4-(2-Bromo-2-propenyl)-4-methyl-gamma-butyrolactone: from the reaction of Ethyl levulinate and (2-Bromoallyl)diisopropoxyborane
  • 4-(2-Bromo-2-propenyl)-4-methyl-gamma-butyrolactone: from the reaction of Ethyl levulinate and (2-Bromoallyl)diisopropoxyborane
  • 4-(2-Bromo-2-propenyl)-4-methyl-gamma-butyrolactone (CAS no.: ), which is also known as 2(3H)-one, 5-(2-bromo-2-propenyl)dihydro-5-methyl-, could be produced through the following synthetic routes.

    A. (2-Bromoallyl)diisopropoxyborane. A flame-dried, 200-mL, three-necked, round-bottomed flask is equipped with a magnetic stirring bar, rubber septum, 125-mL dropping funnel, and an Allihn-type condenser. To the top of the condenser, a 3-L bag, water aspirator through a calcium chloride tube, and allene gas cylinder are connected with two three-way stopcocks as shown in Figure 1. The flask and the bag are evacuated twice using a water aspirator, and filled with allene gas each time. The stopcock between the bag and the reaction flask is closed off, and the flask is cooled to -20°C in a cooling bath made of dry ice and a 9 : 1 mixture of ethylene glycol and acetone . tribromide, BBr3 (25 g, 9.4 mL, 100 mmol) is introduced through the rubber septum via cannula. The stopcock separating the bag from the reaction vessel is then opened. Gas absorption starts immediately and is complete within 10 min to give a dark red solution. When the allene is completely consumed, the gas cylinder is replaced by a nitrogen inlet tube and nitrogen is introduced into the flask. The mixture is stirred at -20°C for 30 min and then 30 mL of dry dichloromethane is added. Next, 33 mL (0.23 mol) of in 50 mL of dry dichloromethane is introduced from the dropping funnel over 1 hr (exothermic!). The mixture is stirred at -20°C for 30 min, then at room temperature for 2 hr, and finally under reflux for 1 hr. The mixture is cooled to room temperature and all volatile components are removed under reduced pressure using a water aspirator. The vessel is filled with nitrogen, and the residue is transferred to a distillation flask via a cannula using nitrogen. Distillation of the residue under reduced pressure gives 16.4-17.1 g (66-69%) of (2-bromoallyl)diisopropoxyborane as a clear liquid, bp 39-43°C (0.4 mm).

    B. 4-(2-Bromo-2-propenyl)-4-methyl-γ-butyrolactone. A flame-dried, 200-mL, three-necked, round-bottomed flask is equipped with a magnetic stirring bar, rubber septum, nitrogen inlet adapter, and a 100-mL dropping funnel. The flask is purged with nitrogen and charged with (2-bromoallyl)diisopropoxyborane (16.2 g, 0.065 mol), prepared above, in 50 mL of dry tetrahydrofuran. The flask is cooled in an ice bath, and ethyl levulinate (9.96 g, 0.069 mol) in 30 mL of dry tetrahydrofuran is added dropwise over 1 hr from the dropping funnel. After the mixture is stirred at 0°C for 1 hr and then at room temperature overnight, it is poured into 50 mL of water and extracted three times with 50-mL portions of ether . The combined organic layers are dried over magnesium sulfate and concentrated using a rotary evaporator. The residue is diluted with 50 mL of dry dichloromethane , and 1 mL of trifluoroacetic acid is added. After the mixture is stirred at room temperature overnight, it is poured into water (50 mL) and the organic layer is separated. The aqueous layer is extracted twice with 100-mL portions of ether . The combined organic extracts are washed with 50 mL of saturated sodium bicarbonate and 50 mL of water, dried over magnesium sulfate, and concentrated using a rotary evaporator. The residue is distilled through a 15-cm Vigreux column under reduced pressure to give 9.22 g (65%) of 4-(2-bromo-2-propenyl)-4-methyl-γ-butyrolactone , bp 88-90°C (0.6 mm), plus 1.9 g of recovered ethyl levulinate, bp 48°C (0.6 mm), and a mixed fraction (0.8 g) containing ethyl levulinate and the product.


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