Enantioselective diethylzinc addition to the exocyclic C{double bond, long}N double bond of some 4-arylideneamino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-one derivatives

Article abstract of DOI:10.1016/j.tetasy.2006.10.013

4-Arylideneamino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 2a-f have been evaluated as substrates in the enantioselective diethylzinc addition reaction in the presence of (1S,2R)-N-alkyl-N-benzylnorephedrines 3a-d as chiral ligands. The utility of using a dual catalytic system (amino alcohol/halosilane) for the diethylzinc addition reaction has been also examined. The addition products 4-(1-arylpropyl)amino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 4a-f were obtained in high yields and with enantiomeric excesses of up to 92%. The treatment of arylimines 2a-f with a diethylzinc reagent did not affect the hetero-ring opening although the C{double bond, long}N double bond of the lateral chain did undergo an addition reaction to yield the C-ethylated products 4a-f. The reductive cleavage of the 1,2,4-triazinyl heterocyclic ring from addition products 4a-f led smoothly to the corresponding free primary amines 5a-f without a significant loss of enantiomeric purity.