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EXAMPLE 2 Rac. 3-benzyloxy-2-methyl-1-propyl bromide A solution of 39 g. (0.216 mole) of rac. 3-benzyloxy-2-methyl-1-propanol and 56.7 g. (0.216 mole) of triphenylphosphine in 216 ml. of dry dimethylformamide was stirred while 11.7 ml. (34.4 g.; 0.216 mole) of bromine was added dropwise, over a 15 min. period, keeping the temperature below 55 C. A few additional drops of bromine were added, until a yellow color persisted. After cooling to 30 C., the reaction mixture was poured into water and hexane was added. The precipitated triphenylphosphine oxide was filtered and washed with hexane. The filtrate and washes were combined and separated into aqueous and organic phases. The aqeuous phase was extracted once with hexane, then the hexane solutions were combined, washed with 10% by weight aqueous NaHSO3 and brine and dried. The organic solution was filtered and concentrated in vacuo giving 44.2 g. of residue which was distilled under high vacuum. There was obtained 42.3 g. of crude bromide as a colorless liquid, b.p. 73- 86 C. (0.05-0.1 mm Hg.). This material was dissolved in benzene and absorbed on 500 g. of silica gel. Elution with 5.2 l. of benzene gave after solvent removal, 38 g. of residue. This material was distilled using a Vigreaux column yielding 37.1. g. (70.7%) of pure rac. 3-benzyloxy-2-methyl-1-propyl bromide as a colorless liquid, b.p. 78-85 C. (0.05-0.1 mm Hg.).
2
[ 63930-46-1 ]
[ 124-63-0 ]
[ 91273-58-4 ]
Yield
Reaction Conditions
Operation in experiment
With N-ethyl-N,N-diisopropylamine; In dichloromethane;
(d) 3-Benzyloxy-2-methyl-1-bromopropane To a -10 solution of 3-benzyloxy-2-methyl-1-propanol (26.4 g., 0.146 mole) and diisopropylethylamine in anhydrous dichloromethane (350 ml.) is added dropwise methylsulfonylchloride (12.46 ml., 1.1 eq.) over a period of 10 minutes. The resulting solution is stirred for 40 minutes at -10. The solution is diluted with additional dichloromethane and washed with water, 1N hydrochloric acid (twice), 1N sodium bicarbonate and brine. After drying (MgSO4), the solvent is removed at reduced pressure to give a bright yellow liquid; Rf =0.58 (silica gel, ether). This is dissolved in 300 ml. of acetone. Lithium bromide (31.92 g., 3 eq.) is added, and the solution is refluxed under argon for 4 hours. The solution is filtered and the filtrate is concentrated. The residue is dissolved in ether and washed with water (twice), 1N sodium bicarbonate (twice), and brine. After drying (MgSO4), the solvent is removed at reduced pressure. An additional 26.4 g. of 3-benzyloxy-2-methyl-1-propanol is treated as described above. The two batches of crude bromide are combined and chromatographed [Waters Prep liquid chromatography System 500, solvent; hexane:dichloromethane (19:1)] and Kugelrohr distilled to give 62.9 g. of 3-benzyloxy-2-methyl-1-bromopropane as a colorless liquid; b.p. 145-148 (0.08 mm of Hg.); Rf =0.75 (silica gel, ether).
(e) 3-Benzyloxy-2-methyl-1-propylmagnesium bromide A mixture of <strong>[91273-58-4]3-benzyloxy-2-methyl-1-bromopropane</strong> (3.35 g., 13.8 mmole) and magnesium turnings (0.58 g., 23.8 mmole) in anhydrous tetrahydrofuran (25 ml.) under argon is irradiated at room temperature with an ultrasonic cleaner for 2.25 hours to give 3-benzyloxy-2-methyl-1-propylmagnesium bromide.
EXAMPLE 3 rac. E-1-benzyloxy-2-methyl-5-hepten-4-ol A slurry of 0.55 g. (0.0236 mole) of magnesium powder in 15 ml. of anhydrous tetrahydrofuran was stirred and heated at reflux while a few drops of a solution of 5 g. (0.0206 mole) of rac. <strong>[91273-58-4]3-benzyloxy-2-methyl-1-propyl bromide</strong> in 30 ml. of anhydrous tetrahydrofuran was added followed by a crystal of iodine. After the Grignard reaction had begun, the remainder of the bromide solution was added dropwise over 35 min. at reflux temperature. The reaction mixture was stirred and heated under reflux for an additional hour then cooled 0-5 C. (ice bath) while a solution of 1.56 g. (0.022 mole) of crotonaldehyde in 15 ml. of anhydrous tetrahydrofuran was added over a 15 min. period. After stirring at room temperature for 2.5 hours, the reaction mixture was poured onto saturated aqueous ammonium chloride and the product was extracted with ether and worked up as in Example 1. The residue (4.62 g.) was chromatographed on 250 g. of silica gel. Elution with 4:1 parts by volume and 2:1 parts by volume hexane-ether gave 3.36 g. of rac. E-1-benzyloxy-2-methyl-5-hepten-4-ol as a pale yellow oil, b.p. 110-120 C. (bath temperature) (0.075 mm Hg.).
EXAMPLE 5 rac. 4-Benzyloxy-3-methylbutyronitrile A solution of 3.38 g. (0.069 mole) of sodium cyanide and 8.4 g. (0.0345 mole) of rac. <strong>[91273-58-4]3-benzyloxy-2-methyl-1-propyl bromide</strong> in 11.5 ml. of water and 45 ml. of ethanol was stirred and heated at reflux for 20 hours. The reaction mixture was cooled, diluted with water and the product was isolated by extraction with benzene and worked up as in Example 1. This afforded 6.4 g. of oily residue which was chromatographed on 350 g. of silica gel. Elution with 4:1 parts by volume and 2:1 parts by volume hexane: ether gave 5.8 g. (89%) of pure rac. 4-benzyloxy-3-methylbutyronitrile as a yellow oil.