Crystal Structure of the Chiral Azomethine Imine, (Z)-(S)-4-(tert-Butylcarbonylamino)-2-(2-methoxybenzylidene)-5-oxopyrazolidin-2-ium-1-ide, Obtained by the Cyclization of tert-Butyl (S)-2-[2-(methoxybenzylidene)hydrazine]-1-(hydroxymethyl)-2-oxocarbamate

Further study of the cyclization reactions of (S)-t-BuOCH2CONHCH(CH2OH)CONHN = Ar, derived from (l)-serine, has found that reaction with MeI/K2CO3 in Me2CO produces (Z)-(S)-4-(tert-butylcarbonylamino)-2-(benzylidene)-5-oxopyrazolidin-2-ium-1-ide, 3. We now wish to report the crystal structure of the 2-methoxybenzylidene derivative, 3a. While the pyrazolyl ring in 3a exhibits an envelope shape, with the flap at C5, the displacement of C5 from the best plane through the ring, however, is only 0.053(5) Å. The dihedral angle between the phenyl and pyrazolyl rings is 12.14(16)°. The pyrazolyl ring has a betaine character with opposite charges on N1 and N2 atoms. The supramolecular arrangement is created from one classical N–H···O and weaker C–H···X (X = O, N) intermolecular hydrogen bonds, each of which generate chains of molecules. Combinations of the (i) C19–H19A···O1 and C11–H11···O2 hydrogen bonds generates sheets of molecules in the ab plane, containing R44(40) rings, (ii) C18–H18B···O1 and C11–H11···O2 hydrogen bonds produce a two molecule wide column, containing R33(26) rings, propagated in the ac plane and (iii) C19–H19A···O1 and C15–H15A···N2 hydrogen bonds generate a different two molecule wide column, containing R33(26) rings, propagated in the ab plane. The compound crystallises in the orthorhombic space group, P212121, with a = 6.5906(5) Å, b = 10.9121(10) Å, c = 22.2080(17) Å, and Z = 4.