Conformational and crystal packing differences in (+)‐7,8‐Di‐tert‐butoxy‐1‐ phenyloctahydro‐1H‐pyrrolo(1,2‐b)‐1H‐phospholo(2,3‐d)isoxazole 1‐oxide diastereoisomers

The crystal and molecular structures of (1S,3aR,7S,8S,8aR,8bR)‐(+)‐7,8‐Di‐tert‐butoxy‐1‐ph‐ enyloctahydro‐1H‐pyrrolo(1,‐b)‐1H‐phospholo(2,‐ d)isoxazole 1‐oxide ( III , hereafter) and (1R,3aS,7S, 8S,8aS,8bS)‐(+)‐7,8‐Di‐tert‐butoxy‐1‐phenyloctahyd‐ ro‐1H‐pyrrolo(1,2‐b)‐1H‐phospholo(2,3‐d)isoxazole 1‐ oxide ( IV , hereafter) have been determined. III crystallizes in space group P2₁2₁2₁, and IV in P2₁ one. The conformational analysis of the puckered heteroatom three‐ring system shows the conformation of noticeable distorted envelope with puckering amplitude Q₂ = 0.397 Å, the intermediate conformation between twisted and envelope with Q₂ = 0.353 Å, and half‐chair conformation with Q₂ = 0.451 Å, for phospholane, oxazolidine, and pyrrolidine rings of III , respectively. Rings in molecule of IV adopt conformations of envelopes with Q₂ = 0.381 Å, Q₂ = 0.367 Å, and Q₂ = 0.363 Å, respectively, for the rings as described above. The molecules of III are assembled by intermolecular weak hydrogen bonds to the one‐dimensional chain along x‐axis. The structure of IV is built‐up of weak intermolecular hydrogen bonds to form a two‐dimensional hydrogen bond network. The differences in conformation between compounds III and IV cause changes in hydrogen bonding pattern, because in molecule IV there is no hydrogen cavern filled with three hydrogen bond donors, and one weak hydrogen bond has not enough strength to force such an arrangement as it is in III . © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:613–620, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20160