Kinetic Resolution by Lithiation: Highly Enantioselective Synthesis of Substituted Dihydrobenzoxazines and Tetrahydroquinoxalines.

Kinetic resolution provided a highly enantioselective method to access a range of 3-aryl-3,4-dihydro-2 H -1,4-benzoxazines using n -butyllithium and the chiral ligand sparteine. The enantioenrichment remained high on removing the tert -butoxycarbonyl (Boc) protecting group. The intermediate organolithium undergoes ring opening to an enamine. The kinetic resolution was extended to give enantiomerically enriched substituted 1,2,3,4-tetrahydroquinoxalines and was applied to the synthesis of an analogue of the antibiotic levofloxacin that was screened for its activity against the human pathogen Streptococcus pneumoniae. [ABSTRACT FROM AUTHOR]