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Yasukochi H, Atago T, Tanaka A, Nakatsuji H, Yoshida E, Kakehi A, Nishii Y, Tanabe Y: Practical, general, and systematic method for optical resolution of gem-dihalo- and monohalocyclopropanecarboxylic acids utilizing chiral 1,1'-binaphtholmonomethyl ethers: application to the synthesis of three chiral pesticides. Org Biomol Chem. 2008 Feb 7;6(3):540-7. Epub 2007 Dec 18.
We performed an efficient practical and systematic optical resolution method for gem-dihalo- and monohalocyclopropanecarboxylic acids and utilizing chiral 1,1'-binaphthol monomethyl ether (R)- as the key auxiliary. Direct esterification of with (R)- gave two 1R- and 1S-diastereomeric esters with marked different R (f) values, both of which were easily separated using simple column chromatography. Monodehalogenation of separated chiral esters using t-BuMgCl and cat. Co (dppe)(2) Cl (2) gave two 1,2-trans- and 1,2-cis-diastereomers with markedly different R (f) values, both of which were similarly separated using simple column chromatography. The obtained diastereomers and were easily hydrolyzed to the desired enantiopure acids (> 99%) and (> 99%), respectively, with recovery of (R)-, both in good to excellent yields. Utilizing the present method, important chiral agrochemicals, carpropamid and fencyclate , were readily synthesized. Pyrethroid with three asymmetric centers was efficiently synthesized in a much better yield compared with the reported method. |
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