Hydrochloric Acid → (9S,10S)-2-chloro-9,10-dihydro-9,10-methano-9-anthracenecarboxylic acid

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Reaction Conditions

Reaction Steps

To a solution of racemic 2-chloro-9,10-dihydro-9,10-methano-9-anthracenecarboxylic acid (100 g; 0.37M) in ethyl acetate (1.5 L) and methanol (75 mL) was added solid (1S,2S)-(+)-pseudoephedrine (61.1 g; 0.37M). With efficient agitation the mixture was warmed to reflux, held for 30 minutes and slowly cooled to 25° C. After a minimum of 2 h the slurry was filtered and washed with ethyl acetate to yield enriched diastereomeric salt (88.6 g; 0.20M; 55%; diastereomeric ratio 80:20, as determined by HPLC). The enriched salt was slurried in 3% methanolic ethyl acetate (2.74 L), warmed to reflux, held 30 minutes,cooled to 25 C. slowly, held 2 h and then filtered and washed with ethyl acetate to provide further enriched salt (70 g; 0.16M; 79%; diastereomeric ratio 95:5, as determined by HPLC). Treatment of the further enriched salt with 5% methanolic ethyl acetate using the same procedure yielded highly enriched salt (60.0 g; 0.14M; 85%; diastereomeric ratio 99:1, as determined by HPLC). This salt (60 g; 0.14M) was added to water (1 L) and the consequent suspension acidified to pH 2-3 with concentrated hydrochloric acid (15 mL) and then extracted with diethyl ether (3×500 mL). The combined organic extracts were washed with brine, dried (MgSO4) and evaporated to an oil. Hexane was added and evaporated to afford enantiomerically enriched acid (36 g; 0.13M; 98% recovery; enantiomeric ratio 99:1, as determined by HPLC) as a white solid. Crystallisation from a mixture of hexane (360 mL) and cyclohexane (720 mL) afforded enantiomerically pure (9S,10S)-2-chloro-9,10-dihydro-9,10-methano-9-anthracene-carboxylic acid as a white solid (30 g, 0.11 mol, 81%) mp 172°-173° C. αD =+101° (c=2.0, CHCl3).

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