2-Diphenylphosphinoyl-l,3-dithiane

X-ray diffraction studies have suggested that the anomeric effect operates in 2-phosphinoyl derivatives of the saturated heterocycles, where the 2-substituent has no lone electron pairs. For example, in 2-diphenylphosphinoyl-l,3-dithiane, the substituent occupies an axial position, in contrast to the 1,3-dioxane and 1,3-oxathiane derivatives, where the same substituent occupies an equatorial position <84JOC3026,88JOC3609,88TL6801>. 

Figure 56. Selected bond lengths in 2-diphenylphosphinoyl-l,3-dithianes 109 and 173e (data from refs. 135 and 340).

Figure 6.72 (a) Predominance of the axial conformation in the conformational equilibrium of 2-diphe-nylphosphinoyl-l,3-dithiane. (b) Chemical equilibration of dimethyl analogues of axial and equatorial 2-diphenylphosphinoyl-l, 3-dithiane. 

Juaristi, E., Valle, L., Valenzuela, B. A., Aguilar, M. A. (1986). Sulfur-carbon-phosphorus anomeric interactions. 4. Conformational analysis of 2-(diphenylphosphinoyl)-l,3-dithiane. Journal of the American Chemical Society, 108(3), 2000. 

A study of the conformation of 2-(diphenylphosphinoyl)-5,5-dimethyl-l,3-dioxane (28), both in solution and in the solid state, and comparisons with similar studies of various 1,3-dithiane analogues have been reported. 1 Certainly in the solid, and probably in solution, the diphenylphosphinoyl group preferentially occupies an equatorial position. 

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