Conformational analysis of p-X-anilino dioxaphosphinanes. Substituent effects on P-31 and N-15 NMR signals and on negative hyperconjugation (n-sigma)

• Published in: Tetrahedron Vol. 66; no. 11; pp. 2066 - 2076
• Main Authors: Dominguez, Zaira, Galvan, Marcelo, Teresa Cortez, Ma, Salas, Magali, Meza, Rocio, Leyva-Ramirez, Marco A., Gordillo, Barbara
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier 13.03.2010
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; X-ray crystal structures; CONSTANTS; CHEMICAL-SHIFTS; SCS and LFER correlations; Negative hyperconjugation; THIOPHOSPHATES; NUCLEAR-MAGNETIC-RESONANCE; Thiophosphoramidates; CRYSTAL; NMR; ENTHALPY; EQUILIBRIUM; Dioxaphosphinanes; COUPLINGS; PHOSPHORUS-HETEROCYCLES; PREFERENCE; Conformation
• ISSN: 0040-4020
• DOI: 10.1016/j.tet.2010.01.034

The conformational analysis of anancomeric cis-ax and cis-eq 2-p-X-anilino-2-thio-4,6-dimethy1-1,3,2 lambda(5)-dioxaphosphinanes (X=OCH3, C6H11, H, Cl, CN and NO2) is informed. In accordance with (3)J(HH), (3)J(HP), (4)J(HP), and (3)J(CP) coupling constants the preferred conformation in solution is a chair in both series of compounds. Structural parameters obtained through X-ray diffraction studies of the series of cis-ax and cis-eq diastereomers 1-6, suggest that the stabilization of the axial and equatorial diastereomers in chair conformation rely on stereoelectronic n(pi)O-sigma*(P-N) and n(pi)N-sigma*(P-O) interactions, respectively. Theoretical Kohn-Sham DFT calculations support the participation of the cited stereoelectronic interactions not only to understand the conformational behavior of these systems but also to give an explanation of the observed substituent-induced chemical shift (SCS) on P-31 and N-15 NMR signals. (C) 2010 Elsevier Ltd. All rights reserved.