ASYMMETRIC NITROGEN - 35. STRUCTURE AND PROPERTIES OF 1(S)-α-CARBOXYETHYL-3,3-BIS(TRIFLUOROMETHYL)DIAZIRIDINE AND ITS DERIVATIVES

Article abstract of DOI:10.1016/S0040-4020(01)88458-1

A second-kind asymmetric transformation involving N-atom inversion has been observed at 20^o for 1(S)-α-carboxyethyl-3,3-bis(trifluoromethyl)diaziridine 1 and its methyl ester 2.X-Ray data for the diastereomer (1S, 2S, α-S), 1A (which is termodynamically preferred in the crystalline phase), ¹H NMR spectra of ethyl ester 3-¹⁵N(1) and 3-¹⁵N(2), CD spectra of 1A,B, 2A,B, potassium salt 4A,B, and semiempirical calculations (MINDO/3 and INDO) for 1A, show that the stereospecificity of crystallization of the diastereomer A is due to the higher energy of the crystal lattice of the diastereomer (1R, 2R, α-S), 1B because of hindered charge compensation as well as to the hindrance by the CF3 groups to intermolecular H-bonds.According to semiempirical calculations, the stability of 3,3-bis(trifluoromethyl)-diaziridines (TFD) to the action of electrophiles is due to the lowering of the n- and w-orbital energies and depolarization of the C-N bonds due to hyperconjugation and the inductive effect of the CF3-groups.The steric effect of these groups is the reason of the low configurational stability of TFD compared with the 3,3-dimethyl analogues.