Stereochemistry of chiral pentacoordinate spirophosphoranes correlated with solid-state circular dichroism and 1H NMR spectroscopy

Two sets of diastereomers of pentacoordinate spirophosphoranes separately derived from l-valine (or d-valine) and l-leucine (or d-leucine) were synthesized, isolated, and structurally characterized both in the solid state (X-ray crystallography and solid-state CD spectroscopy) and in the solution (1H NMR). The Λ and Δ absolute configurations of a pair of enantiomers 3a and 4a with distorted trigonal bipyramids (TBPs) geometry are directly determined by X-ray diffraction analysis, respectively. The chiral-at-phosphorus features of the related diastereomers were correlated with their solid-state CD and 1H NMR spectra.

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(3S,5Λ,8S)-3,8-Di(propan-2-yl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC10H19N2O4P[α]D20=-60.3 (c 1.0, DMSO)Absolute configuration: (3S,5Λ,8S)

(3S,5Δ,8S)-3,8-Di(propan-2-yl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC10H19N2O4P[α]D20=+22.6 (c 1.0, DMSO)Absolute configuration: (3S,5Δ,8S)

(3R,5Δ,8R)-3,8-Di(propan-2-yl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC10H19N2O4P[α]D20=+60.1 (c 1.0, DMSO)Absolute configuration: (3R,5Δ,8R)

(3R,5Λ,8R)-3,8-Di(propan-2-yl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC10H19N2O4P[α]D20=-22.6 (c 1.0, DMSO)Absolute configuration: (3R,5Λ,8R)

(3S,5Λ,8S)-3,8-Bis(2-methylpropyl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC12H23N2O4P[α]D20=-55.7 (c 1.0, acetone)Absolute configuration: (3S,5Λ,8S)

(3S,5Δ,8S)-3,8-Bis(2-methylpropyl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC12H23N2O4P[α]D20=+31.7 (c 1.0, acetone)Absolute configuration: (3S,5Δ,8S)

(3R,5Δ,8R)-3,8-Bis(2-methylpropyl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC12H23N2O4P[α]D20=+55.4 (c 1.0, acetone)Absolute configuration: (3R,5Δ,8R)

(3R,5Λ,8R)-3,8-Bis(2-methylpropyl)-1,6-dioxa-4,9-diaza-5λ5-phosphaspiro[4.4]-nonane-2,7-dioneC12H23N2O4P[α]D20=-31.9 (c 1.0, acetone)Absolute configuration: (3R,5Λ,8R)