Development and applications of novel chiral auxiliaries powerful for both enantioresolution and determination of absolute configuration by X-ray crystallography

Recently, there is a great demand for various chiral organic compounds with 100% e.e. To obtain enantiopure chiral compounds and to determine their absolute configurations in an unambiguous way, it is convenient to take the method of enantioresolution employing chiral auxiliaries. We report here the development and applications of novel chiral auxiliaries powerful for both enantioresolution and determination of absolute configuration. The chiral auxiliary, (1S,2R, 4-R)-(-)-2,10-camphorsultam 5, is useful for enantioresolution of various carboxylic acids by HPLC on silica gel and also for X-ray crystallographic determination of their absolute configurations. Furthermore, we have succeeded in extension of this strategy to various alcohols by designing a new chiral auxiliary connecting (1S,2R,4R)-2,10-camphorsultam moiety and carboxylic acid group. Namely, chiral phthalic (-) -1 and dichlorophthalic (-) -2 acids were allowed to react with racemic alcohols, and the diastereomeric mixture of esters obtained was separated by HPLC on silica gel. These diastereomers generally crystallized as large prismatic crystals suitable for X-ray diffraction, and their absolute configurations could be determined by the X-ray crystallographic method using the camphor part as the internal reference of absolute configuration. The method using these chiral phthalic and dichlorophthalic acids has been applied to various racemic alcohols to obtain enantiopure alcohols and also to determine their absolute stereochemistry.