l-selectridereg;; tetrahydrofuran; ethanol;
reactants are commercially availlable.
tridgett, robert, wo2005/77946, a1, (2005) 1m l-selectridex in tetrahydrofuran (135 ml, 135 mmol, 2.87 eq. ) was added slowly over 30 minutes to a stirred solution oftetrabenazine rr/ssracemate (15 g, 47 mmol) in ethanol (75 ml) and tetrahydro furan (75 ml) at 0 °c. after addition was complete the mixture was stirred at 0 °c for 30 minutes an d then allowed to warm to room temperature. the mixture was poured onto crushed ice (300 g) and wate r (100 ml) added. the solution was extracted with diethyl ether (2 x 200 ml) and the combined ethereal extracts washed with water (100 ml) and partly dried over anhydrous potassium carbonate. drying w as completed using anhydrous magnesium sulphate and, after filtration, the solvent was removed at re duced pressure (shielded from the light, bath temperature <20 °c) to afford a pale yellow solid. the solid was slurried with petroleum ether (30-40 °c) and filtered to afford a white powdery solid (12 g, 80percent).; 2a. preparation of 2 3-dehydrotetrabenazine; a solution containing a racemic mixtur e (15 g, 47 mmol) of rr and ss tetrabenazine enantiomers in tetrahydrofuran was subjected to reduction with l- selectridee by the method of example 1a to give a mixture of the 2s, 3r, 1 lbr and 2r, 3s , 1 lbs enantiomers of dihydrotetrabenazine. as a white powdery solid (12 g, 80percent). the partially purified dihydrotetrabenazine was then dehydrated using pcl5 according to the method of example 1 b to give a semi-pure mixture of 1 lbr and 1 lbs isomers of 2, 3-dehydrotetrabenazine (the 1 lbr enantiomer of which is shown below) as a yellow solid (12.92 g, 68percent).
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