Asymmetric synthesis of (+)- and (−)-deoxyfebrifugine and deoxyhalofuginone

Both enantiomers of deoxyfebrifugine (4) and deoxyhalofuginone (5), analogues of the quinazolinone-containing biologically active compounds febrifugine (1) and halofuginone (3), have been prepared in a six-step reaction sequence featuring an organocatalyzed Mannich reaction as the key stereo-inducing step. The compounds were isolated as their dihydrobromide salts in 29–42% overall yield and in 74–80% enantiomeric excess.