BETA-ALKOXY SCHIFF-BASE OXAZOLIDINE TAUTOMERISM - SOLID-STATE STRUCTURE OF N-DIPHENYLMETHYLENE-L-THREONINE METHYL-ESTER

The benzophenone Schiff base of methyl L-threonate, C18H19NO3, M(r) = 297.36, crystallized as its cyclic methyl -methyl-2,2-diphenyl-1,3-oxa zolidine-4-carboxylate tautomer, orthorhombic, P2(1)2(1)2(1), a = 8.45 5 (2), b = 12.648 (2), c = 14.650 (3) angstrom, V = 1566. (5) angstrom 3, Z = 4, D(x) = 1.26 g cm-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 0.8 cm-1, F(000) = 632, T = 296 K. The structure was solved by dire ct methods; R = 0.040 and wR = 0.045 for 1113 observed reflections. H atoms were included in the refinement, but were constrained to their a ttached atoms. The amine hydrogen (HN) was located from a difference m ap and was refined with a fixed isotropic thermal parameter. The struc ture confirms the existence of the oxazolidine tautomer in the solid s tate and shows that the oxazolidine nitrogen is sp3 hybridized with a fixed Walden configuration. In the crystal there is no obvious hydroge n bonding to HN, or to the nitrogen lone pair, although the N-H bond i s directed toward the center of a phenyl ring on an adjacent molecule (perpendicular H atom-ring distance 3.09 angstrom).