Synthesis and structure of trans-(+)-(3S,4S)-3-amino-4-ferrocenyl-1-p-methoxyphenylazetidin-2-one

trans-(+)-(3S,4S)-3-Amino-4-ferrocenyl-1-p-methoxyphenylazetidin-2-one (I) was obtained with >99% e.e. applying lithium chiral ester enolate-imine condensation strategy. The X-ray structure was determined in order to establish unambigously both absolute and relative configurations at the stereogenic centers C11 and C12. The final value of the freely refined Flack parameter, x=−0.007(11), confirmed the S configuration at both stereogenic centers C11 and C12. The azetidin-2-one ring and the methoxyphenyl moiety revealed a static disorder with the two slightly different, but clearly resolved conformations with the partial population factors close to 0.5 (conformations A and B). The ferrocene subunit and the atom C11 which is attached directly to the cyclopentadiene of the ferrocene moiety, on the other hand, reveal unique crystallographic positions throughout the structure. The crystal structure determination confirmed the trans-arrangement of the substituents with respect to the bond C11-C12 (torsion angle C6-C11-C12-N2 is 121.5(15)° in conformation A and C6-C11-C12A-N2A is 125(6)° in conformation B). The non-bonded interactions governing crystal packing are present only between the molecules of the identical conformation. Consequently, two separated crystal packing conceptions are present in the structure, and none of the non-covalent interactions was observed between them. Hydrogen bonding patterns between those two packings are rather different: while molecules of the conformation A form hydrogen-bonded dimers via N2-H2B⋯O1 bond, those of the conformation B form endless double chains via N2A-H2A3⋯O2A and N2A-H2A2⋯O1A bonds.