ISSN:
1042-7163
Keywords:
Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Results of IR and 1H, 13C, and 31P NMR studies of the anancomeric title compounds (2-5) and compound 1 (Scheme 1) are analyzed to search for the existence of high-energy boat or twist-boat conformations in the equatorial epimers. While the difference in frequencies (Δν)P=O between the axial and equatorial compounds and 13C NMR JPOCC and anti JPOCCH3 values suggest the participation of twist-boat conformations for the equatorial isomers, coupling constants in 1H NMR JH4H5a or JH6H5a and JH4H5e or JH6H5e of the equatorial isomers 2e-4e along with the lack of a large 3JPH in 31P NMR are consistent with predominant chair conformations. In addition, an X-ray structure of the equatorial 2-p-nitrophenoxy-2-oxo-cis-4,6-dimethyl-1,3,2-dioxaphosphorinane (4e) showed that the molecule adopts a chair conformation with no severe ring flattening in the OPO region in the solid state. X-ray structures of trans-4 and trans-5 displayed chair conformations with mild ring flattening especially in the axial methyl region, presumably as a result of the steric methyl-oxygen interaction. CPMAS 13C and 31P NMR spectra of 4a and 4e provide evidence against the presence of a significant contribution of a twist-boat conformation in solid equatorial 4e. The NMR spectral analysis of 1e, on the other hand, suggests a substantial contribution of a twist conformation as well as, possibly, some contribution of the inverted chair. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8:509-516, 1997
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
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