A Convenient Synthetic Route to Differentially Functionalized Long Chain Polyethylene Glycols

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• 3,4-Dihydro-2H-pyran (7.1 g, 84.7 mmol) was added dropwise to a solution of 2-(2-chloroethoxy)ethanol (8.8g, 70.6 mmol) and the mixture was stirred for 4 hours at room temperature. Solid sodium hydrogencarbonate (2g) was added, the reaction mixture was filtered through Celite and washed with ether. The product 3 was purified by vacuum distillation (b.p. 50–60°C, Kügelrohr, 0.2 mmHg) and obtained as a clear liquid (12.3g, 80%)
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• In a typical reaction, benzyl-pentaethylene glycol-THP, 8, (2.95g, 7.19 mmol) was stirred in a mixture of methanol and dichloromethane (1:1 ratio, 50 ml) with a catalytic amount of concentrated hydrochloric acid for 8 hours. Sodium hydrogencarbonate (1g) was added and the mixture then filtered. The solvent was removed under reduced pressure and the resultant clear oil purified by flash chromatography (ethyl acetate as the eluent) to give monobenzyl-pentaethyleneglycol as a colorless clear oil (2.00g, 6.07 mmol, 85%)
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• In a typical reaction, benzyl-hexaethyleneglycol-THP, 9, (1.27g, 2.78 mmol), 10% Pd/C (0.1 eq.) in absolute ethanol (40 ml) was stirred under hydrogen for 3 hours at room temperature. The reaction mixture was filtered thought a plug of Celite, and the solvent removed by reduced pressure. The crude product was purified by flash chromatography (eluted with 5% MeOH in CH2Cl2) to afford pure 13 as a clear oil (0.75g, 74%). Analytical data for 13; 1H NMR, (200 MHz, δ, ppm) 1.5–1.7 (m, 6H, THP), 3.57–3.74 (m, 22H, O-CH2CH2-O), 3.81–3.90 (m, 2H, OTHP), 4.62 (t, 1H, THP); elemental analysis C, 55.3; H, 9.6; calc'd (for C17H34O8) C, 55.72; H, 9.37
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