V. SEHGAL, P. SINGH, A. DANDIA AND R. BOHRA 1159 Letcher, R. M., Lai, T. F. & Mak, T. C. W. (1985). J. Chem. Soc. Perkin Trans. 1, pp. 1921-1926. Paillous, N., Forgues, S. F., Jaud, J. & Devillers, J. (1987). J. Chem. Soc. Chem. Commun. pp. 578-579. Acta Cryst. (1994). C50, 1159-1161 1-Acetyl-5-benzyl-2-methylthio-5H-imidazol- 4-one M. F. MACKAYAND G. J. TRAr~TINO Department of Chemistry, La Trobe University, Bundoora, Victoria 3083, Australia The atoms of the imidazolone ring are coplanar to within 0.038 (5) A, but there is a slight degree of ring pucker, as reflected in the ring torsion angles (Table 2); the acetyl group at N(1) lies close to the ring plane [torsion angle C(5)--N(1)--C(I')---C(I") 2.6 (4)°], while the S---CH3 group at C(2) is twisted by about 7 ° from it. The benzyl group at C(5) adopts an orientation relative to the imidazolone moiety as defined by the torsion angles C(4)--C(5)--C(5')-- C(6') of 57.1 (3) ° and C(5)--C(5')--C(6')--C(7') of 81.9 (3) ° . The two rings face each other, the dihedral angle between their perpendiculars being 53.4 (3) ° (see Fig. 2). When compared with other 2-thiohydan- toin derivatives (Lempert, Nyitrai, Zauer, Kfilm~m, Argay, Duisenberg & Sohar, 1973; Ki6c- Kononowicz, Zejc, Mikolajczyk, Zatorski, Karolak- B. M. DUGGANAND J. F. K. WZLSnmE CSIRO, Division of Biomolecular Engineering, Parkville, Victoria 3052, Australia (Received 15 July 1993; accepted 23 November 1993) Abstract Atoms of the imidazolone ring in the title com- pound, Cl3HlaN202S, are approximately coplanar. The N(1) acetyl group lies close to the plane while the C(2) methylthio substituent is twisted by about 7 ° from it. The imidazolone and phenyl rings face each other, the dihedral angle between their perpen- diculars being 53.4 (3) ° . Comment The methylation of 1-acetyl-5-benzyl-2-thioxoimi- dazolidin-4-one [N-acetylphenylalanine thiohydan- toin (1), R = H] by means of diazomethane has been studied, and the reaction, experimental details of which will be reported elsewhere, found to give two isomers, namely the N-methyl isomer [(1), R = CH3] and the S-methyl isomer (2). The structure of the former isomer was established by means of its 1H NMR spectrum (the relevant spectroscopic data will be presented elsewhere) as 1-acetyl-5-benzyl-3- methyl-2-thioxoimidazolidin-4-one [(1), R = CH3]. The structure of the latter isomer was shown by X-ray analysis to be 1-acetyl-5-benzyl-2-methylthio- 5H-imidazol-4-one (2). 1 .5 CH3CO,N--(~HCH 2C6 H 5 2 I L4 s~C~-N,-C~o R 1 5 OH3CON--CHCH 2C6 H5 21 I. c c CH3S / ~N I ~'O (1) (2) © 1994 International Union of Crystallography Printed in Great Britain - all rights reserved ( 7' S(2') N(1) ' 11' b Fig. 1. Perspective view of (2) (3R enantiomer) with displacement ellipsoids scaled to 50% probability. The C symbol for C atoms is omitted and H atoms are denoted by spheres of arbitrary radii. i C cr ( J ,,(3 Fig. 2. Stereoview of the crystal packing, projected along a with the b axis vertical. Acta Crystallographica Section C ISSN 0108-2701 ©1994