Chiral synthesis via organoboranes. XVI. Boroxazolidones derived from α-amino acids and borinic or boronic esters. A simple procedure for upgrading borinates and boronates to materials of high optical purity
The synthesis of boron heterocycles from borinic and boronic esters with α-amino acids was explored as a means of upgrading the optical purities of intermediates from asymmetric hydroboration.B-Methoxy-9-borabicyclononane, methyl dicyclohexylborinate and (+)- and (-)-methyl diisopinocampheylborinate react with various α-amino acids to form the corresponding crystalline chelates.Recrystallization of the chelates derived from methyl trans-2-phenylcyclopentylisopinocampheylborinate of 85percent ee with l-phenylalanine, methyl isopinocampheyl-exo-norbornylborinate of 83percent ee with l-proline and both optical isomers of methyl diisopinocampheylborinate of 92percent ee with l-proline yield the corresponding products with optical purities approaching 100percent ee.Dimethyl cyclopentylboronate, dimethyl exo-norbornylboronate and dimethyl isopinocampheylboronate upon treatment with iminodiacetic acid and N-methyliminodiacetic acid form the corresponding bicyclic boronates.Recrystallization of the chelate derived from diethyl 3-tetrahydropyranylboronate and iminodiacetic acid yields a product of essentially 100percent ee.Consequently formation of boroxazolidones of asymmetric hydroboration products provides one possible route to upgrade such products to materials of high optical purity.
Brown, Herbert C.,Gupta, Ashok K.
p. 73 - 82
(2007/10/02)
More Articles about upstream products of 117256-66-3