The reaction of (4R,5R)- and (4S,5S)-4,5-epoxy-2(E)-hexenoates and secondary amines

A reaction of methyl (4R,5R)-4,5-epoxy-2(E)-hexenoate 1 with N-benzylmethyl amine gave a diastereomerically pure methyl (4R,5R)-4,5-epoxy-(3S)-N-benzyl methylamino hexanoate 6 and methyl (4S,5R)-4-N-benzylmethylamino-5-hydroxy- 2(E)- hexenoate 7. The former was chemoenzymatically converted to (-)-osmun dalactone 11, which is an aglycone of osmundalin. On the other hand, the di rectly conjugated addition of dimethylamine to methyl (4S,5S)-4,5-epoxy-2(E )-hexenoate 1 followed by treatment with MeOH at 40 degreesC exclusively pr ovided methyl (4R,5S)-4-dimethylamino-5-hydroxy-2(E)-hexenoate 16, which wa s converted into L-(-)forosamine 18.