CRYSTAL AND MOLECULAR-STRUCTURES OF ISOMERIC ORPHOLINO-2-THIONO-4-METHYL-1,3,2-DIOXAPHOSPHINANE AND 2-MORPHOLINO-2-OXO-4-METHYL-1,3,2-DIOXAPHOSPHINANE

Two isomeric pairs of compounds, cis- and rpholino-2-thiono-4-methyl-1 ,3,2-dioxaphosphinane, (1A + 1B) and 2-morpholino-2-oxo-4-methyl-1,3,2 -dioxaphosphinane (2A + 2B) were obtained and separated into the pure compounds by silica gel chromatography. Attempts at crystallization af forded 1A, 1B, and 2B. Each crystalline isomer was studied by the X-ra y technique, and each crystal and molecular structures assigned. These studies revealed that 1B and 2B have exocyclic 4-CH3 and sulfur (for 1B) or 4-CH3 and oxygen (for 2B) in the diequatorial position (cis-geo metry), while compound 1A possesses the 4-CH3 group in equatorial posi tion while sulfur is in an axial position (trans-geometry). For all th e examined compounds, all the basic geometrical parameters, such as bo nd lengths, bond and torsion angles, and the deformation of a chair co nformation of the six-membered heterocyclic rings, have been establish ed. Such unambiguous assignment of cis-trans geometry in both pairs of 1 and 2 allowed us to confirm the stereoretentive PS --> PO conversio n 2 by means of OXONE(R) and the stereoinvertive mechanism of formic-a cid catalyzed hydrolysis of phosphorothiomorpholidates. (C) 1998 John Wiley & Sons, Inc.