The crystal and molecular structures of the diastereomeric (4Z)- and (4E)-3-oxo-2,3-dihydrobilatrienes-abc

The molecular and crystal structures of two diastereomeric 3-oxo-2,3-dihydrobilatrienes-abc1 and2 are determined at low (1, 2) and room temperature (2). The configurations at the exocyclic double bond in position 4 are found to be (Z) for1 and (E) for2. Tautomerism, conformation and crystal packing of1 and2 can be understood on the basis of the pattern of intra- and intermolecular hydrogen bonds. Compared to1, a more open helix conformation is found for the (E) diastereomer2. An analysis of crystallographically observed temperature factors of2 yields the result that the highest flexibility is found for the saturated lactam ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.