3-(6-Methyl-2-pyridyl)-2-phenyl-3,4-dihydro-1,3,2-benzoxazaphosphinine 2-oxide

In the title compound, C19H17N2O2P, the six-membered 1,3,2-oxazaphosphinine ring adopts a boat conformation with the phosphoryl O atom in an equatorial position. The dihedral angle between the 6-methyl-2-pyridyl and phenyl groups is 75.5 (1)°. These substituents are trans to each other, and are oriented at angles of 57.2 (1) and 74.8 (1)°, respectively, to the benzene ring. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds. The phosphoryl O atom participates in intermolecular C—H⋯O interactions with the neighbouring molecules, forming centrosymmetric R 2 2(14) dimers.

In the title compound, C 19 H 17 N 2 O 2 P, the six-membered 1,3,2oxazaphosphinine ring adopts a boat conformation with the phosphoryl O atom in an equatorial position. The dihedral angle between the 6-methyl-2-pyridyl and phenyl groups is 75.5 (1) . These substituents are trans to each other, and are oriented at angles of 57.2 (1) and 74.8 (1) , respectively, to the benzene ring. The crystal structure is stabilized by intra-and intermolecular hydrogen bonds. The phosphoryl O atom participates in intermolecular C-HÁ Á ÁO interactions with the neighbouring molecules, forming centrosymmetric R 2 2 (14) dimers.
MK thanks the University Grants Commission, New Delhi, for sanctioning the major project for this work.

Comment
As organophosphorus compounds are ubiquitous, they have found multifaceted applications in nature. They can be used as insecticides and herbicides (Hoagland et al., 1988), fungicides (Smith et al., 1983), plant growth regulators and present also antifungal activity (Molodykh et al., 1990). The significant activity of all these compounds was accredited to the presence of six membered heterocyclic rings. In view of these activities, the title compound, (I), has been studied, as a part of our ongoing investigation to find out the influence of different substituents on the conformation of the heterocyclic ring.

Experimental
A solution of phenylphosphonic dichloride (0.002 mol) in 25 ml of dry THF was added dropwise over a period of 20 min. to a stirred solution of 2-{[(6-methyl-2-pyridyl)amino]methyl}phenol (0.002 mol) and triethylamine (0.004 mol) in 30 ml of dry THF. After completion of the addition, the temperature of the reaction mixture was slowly raised to room temperature and stirred for 30 min. The reaction mixture was then heated to 318-323 K and maintained at that temperature for 3 h.
under stirring. Completion of the reaction was monitored by TLC analysis. Triethylamine hydrochloride was filtered from the reaction mixture and the solvent was removed under reduced pressure. The crude product was purified by column chromatography on silica gel (100-200 mesh, ethyl acetate:hexane) to afford pure product. Transparent, colorless plate-shaped single crystals are obtained by slow evaporation of a 2-proponal solution.