engleski

Synthesis and structure determination of methyl (3S)- and (3R)-(trans-(3'R, 4'R)-3-amino-1-(4-methoxyphenyl)-2-oxo-4-phenylazetidin-3-yl)-2, 2-dimethyl-3-ferrocenylpropanoate

Lewis acid (ZnI2) - promoted Mannich reaction of azetidin-2-one - tethered aldimine 3 with silylenol ether 4 in toluene at - 20 oC afforded a diastereomeric mixture of beta-amino acid esters 5 and 6 in ratio 65:35. Diastereomers 5 and 6 were chromatographycally separated and their crystal structure determined in order to establish unambigously both absolute and relative configurations at the stereogenic centers C11, C12, and C14. The final value of the freely refined Flack parameter of diastereomer 6, x = -0.003 (3), unambigously indicates that all three centers have the R configuration. According to the synthetic procedure, configurations on C12 and C14 of diastereomer 5 have the same R orientation as of diastereomer 6, therefore Friedel pairs for the structure of 5 were not measured. Furthermore, S configuration on C11 of diastereomer 5 was assigned in relation to R configuration at C12 and C14 stereogenic centers.

Asymmetric Mannich reaction ; beta-Lactam ; Ferrocene ; Imine ; Lewis acid ; X-Ray structure

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