Conformational analysis of 2-OAryl-2-oxo-4,6-dimethyl- and -4-methyl-1,3,2λ5-dioxaphosphorinanes. Spectroscopic, X-Ray, and solid-state 13C and 31P studies

✍ Scribed by Ernest L. Eliel; Barbara Gordillo; Peter S. White; David L. Harris

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 263 KB
• Volume: 8
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1997)8:6<509::aid-hc9>3.0.co;2-1

✦ Synopsis

Results of IR and 1 H, 13 C, and 31 P 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 (Dm) P‫ס‬O between the axial and equatorial compounds and 13 C NMR J POCC and anti J POCCH3 values suggest the participation of twist-boat conformations for the equatorial isomers, coupling constants in 1 H NMR J H4H5a or J H6H5a and J H4H5e or J H6H5e of the equatorial isomers 2e-4e along with the lack of a large 3 J PH in 31 P 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-1,3,2dioxaphosphorinane (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 Dedicated to Prof. William E. McEwen on the occasion of his seventy-fifth birthday.