Asymmetric Synthesis of 2-(α-Aminoalkyl)oxazoles, 2-Oxazolylpyrrolidines, 2-Oxazolylpiperidines: Total Synthesis of 4,5-Dihydroxypipecolinic Acid

Asymmetric α-alkylation of 2-aminomethyl-4,5-diphenyloxazole was achieved by formation of azomethines 1 and ent-1 with the enantiomers of 2-hydroxypinan-3-one as chiral auxiliaries, reaction with alkylating reagents and final removal of the chiral auxiliary giving rise to optically active 2-(α-aminoalkyl)oxazoles 3, ent-3, 6 and 9. If α,ω-dihaloalkanes were used the resulting alkylation products could be further cyclized by intramolecular alkylation of the amino group to afford optically active 2-oxazolyl-N-heterocycles 4, ent-4, 7 and 10. The latter could be used for the total synthesis of naturally occurring 4,5-dihydroxypipecolinic acid 13.

2-(1-aminoalkyl)-1,3-oxazoles - asymmetric synthesis - 2-oxazolylpiperidines - 2-oxazolylpyrrolidines - 4,5-dihydroxypipecolinic acid - chiral auxiliaries - heterocycles