Conformational analysis of six-membered ring dioxaphosphinanes. Part 1: Anancomeric thiophosphates

• Published in: Tetrahedron Vol. 60; no. 48; pp. 10927 - 10941
• Main Authors: Hernández, Javier, Ramos, Rafael, Sastre, Noé, Meza, Rocío, Hommer, Herbert, Salas, Magali, Gordillo, Barbara
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 22.11.2004; Elsevier
• Subjects: Chemistry; Chemistry, Organic; Conformation; Dioxaphosphinanes; LFER correlations; NMR; Physical Sciences; Science & Technology; Thiophosphates; X-ray crystal structures; X-ray crystal structures; LFER correlations; NMR; Dioxaphosphinanes; Thiophosphates; Conformation; PHOSPHATE; C-13; NMR-SPECTRA; RESONANCE; P-31 CHEMICAL-SHIFTS; conformation; thiophosphates; dioxaphosphinanes; COUPLING-CONSTANTS
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2004.09.025

A study of the conformation of a series of anancomeric axial and equatorial 2-aryloxy-2-thio-1,3,2λ 5-dioxaphosphinanes 2– 12 in solution and solid state is reported. In accord to the stereoelectronic theory, aryl thiophosphates substituted with electron-withdrawing (EW) groups will tend to occupy axial positions in chair ring conformations due to the stabilizing endo-anomeric ( n πO–σ P–X *) hyperconjugative interaction. The antiperiplanar orientation of the orbitals involved in the stereoelectronic interaction is a requirement that is fulfiled in the axial series of compounds when the ring adopts a chair conformation. Therefore, in the equatorial series of thiophosphates, the axial seeking characteristics of aryloxy-EW groups might render the molecule with distortion of the chair conformation. An opposite trend is anticipated for the less axial seeking aryl thiophosphates substituted with electron releasing (ER) groups. A detailed analysis of the 3 J HH, 3 J PH and 3 J CP coupling constants allowed us to conclude that there is no contribution of high energy twist-boat conformations in the equatorial thiophosphates substituted with aryl-EW groups in solution. In consequence, single chair conformations were found in solid state for aryl thiophosphates in both configurations. X-ray geometrical analysis of bond distances and bond angles supports clearly the participation of hyperconjugative endo-anomeric ( n πO–σ P–OAr *) effect in the stabilization of axial series of compounds and the participation of endo-anomeric ( n πO–σ P S *) effect in the stabilization of the equatorial thiophosphates in chair conformations. The conformation of a series of axial and equatorial anancomeric aryl thiophosphates is analyzed in terms of the anomeric n πO–σ P–OAr * and n πO–σ P S * endo-hyperconjugative interactions.