5,5-Dimethyl-2-methylseleno-1,3,2-dioxaphosphorinan-2-one

The title compound, C6H13O3PSe, was obtained in the reaction of 5,5-dimethyl-2-oxo-2-seleno-1,3,2-dioxaphosphorinane potassium salt with methyl iodide. The selenomethyl group is in the axial position in relation to the six-membered dioxaphosphorinane ring.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: DN2544).
In our previous study (Cholewinski et al., 2009) we described a correlation between the anomeric iteractions n O → σ* P-X (where X is O or NH) and axial / equatorial conformer distribution in >P(Se)XR systems. However, those orbital systems were different -contained single P-X bond and the selenium atom was linked only to P atom, formally by a double bond.
The reasoning derived there cannot be applied to prediction of conformation for systems with double P=O and single P-Se bonds, like the present case or to bisselenides. In fact, the doubly bonded oxygen atoms tend to occupy equatorial position in relation to the six-membered ring.

Refinement
Hydrogen atoms were placed in calculated positions and refined using a standard riding model. C-H bond lengths were set to 0.99 and 0.98 Å and U iso (H) were set to 1.5 and 1.2 U eq (C) for CH 3 and CH 2 groups, respectively.
The residual electron density peak is 0.83 Å from SE1, the deepest electron density hole is 1.28 Å from H5A. Absolute structure determination is unequivocal because only 189 Bijvoet pairs were measured. As the structure is not chiral, we did not attempt to elucidate it further. Fig. 1. The nolecular structure of (I), with the atom labeling scheme. Displacement ellipsods are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii.

5,5-Dimethyl-2-methylseleno-1,3,2-dioxaphosphorinan-2-one
Crystal data Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )