Crystallization-based optical resolution of 1,1′-binaphthalene-2,2′-dicarboxylic acid via 1-phenylethylamides: control by the molecular structure and dielectric property of solvent

In the recrystallization of a diastereomeric mixture of amides {RSa,S)-1 formed from racemic 1,1'-binaphthalene-2'-dicarboxylic acid and (S)-1-phenylethylamine, either of the diastereomers crystallizes Out as a diastereomerically pure term, depending on the solvent employed: sterically undemanding solvents, acetone, dichloromethane, and acetonitrile, afford crystals formulated as (S-a,S)-1 solvent with an exception of ethanol, which affords (R-a,S)-1 center dot EtOH, while sterically bulkier solvents afford (R-a,S)-1 including no solvent, The stereoselectivity can be rationalized by the crystal structures. A dielectrically controlled resolution (DCR) can also be can tied out by using, mixed solvents, which contain, for example, 25 vol % of acetone and varying rations of hexane and 4-piopanol in total 75 vol %; (S-a,S)-1 acetone is deposited as crystals from the solvents with a dielectric constant (epsilon) range 8.9-epsilon-10.2, while (R-a,S)-1 is deposited from the solvents with 14.8-epsilon-20.3. (C) 2009 Elsevier Ltd. All rights reserved.