C11H15NO5S, monoclinic, P21/n (no. 14), a = 10.2184(9) A, b = 10.1462(6) A, c = 13.183(1) A, ) = 112.716(7)°, V = 1260.8 A, Z = 4, Rgt(F) = 0.031, wRref(F) = 0.085, T = 173 K. Source of material To a solution of 3.06 mmol (1.0 g) 2-isopropyl-4-methyl-3(toluene-4-sulfonyl)oxazolidine carboxylic acid [1] in 10mlTHF were added 5 ml of hydrobromic acid (24 % aqueous solution). The mixture was stirred at room temperature for 30 min and then stirred for further 12 h at 60 °C. The organic solvent was removed under reduced pressure and 10 ml of water were added. The mixture was stirred for further 10 min. The aqueous phase was extracted with diethyl ether (3 × 20 ml) and the organic layers were dried (MgSO4). After removal of the solvent the oily residue was dissolved with 10 ml diethyl ether and stored for 12 h at –18.°C for crystallization (yield 60 %). Experimental details H1, H4 and H5 bound to nitrogen and oxygen atoms were found in the difference Fourier map and refined without position constraints and with Uiso(H) = 1.2 Ueq(N,O). The other hydrogen atoms were added to the model in calculated positions with Uiso(H) = 1.2.Ueq(C). Discussion The title compound is the product of the acetal cleavage of 2isopropyl-4-methyl-3-(toluene-4-sulfonyl)oxazolidine-4carboxylic acid. Themolecule crystallizes as a racemicmixture in the centrosymmetric space group. Themolecules are linked viaH bonds (O1···O5···O4; i: –x+1⁄2,y+1⁄2,–z+1⁄2; ii: –x+1⁄2,y–1⁄2,–z+1⁄2) forming a double chain along [010]. These double chains are further linked by very weak N–H···O interactions (d(N···O) = 3.165(2) A). Similar structures bearing the 3,5-dihydroxyhexan2-one moiety instead of the tosyl-group occurs in natural products, e. g., conagenin [2]. Z. Kristallogr. NCS 225 (2010) 139-140 / DOI 10.1524/ncrs.2010.0059 139 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: colorless block, size 0.09 × 0.13 × 0.51 mm Wavelength: Mo K+ radiation (0.71073 A) .: 2.70 cm−1 Diffractometer, scan mode: STOE IPDS 2, rotation method 2,max: 50.32° N(hkl)measured, N(hkl)unique: 7892, 2231 Criterion for Iobs, N(hkl)gt: Iobs > 2 ((Iobs), 1999 N(param)refined: 174 Programs: SHELXS-97 [3], SHELXL-97 [4], ORTEP-3 [5] Table 1. Data collection and handling. H(2A) 4e 0.1150 0.3543 −0.1523 0.041 H(3A) 4e 0.1572 0.3641 −0.3145 0.049 H(5A) 4e 0.4860 0.1102 −0.1862 0.058 H(6A) 4e 0.4491 0.1032 −0.0226 0.050 H(7C) 4e 0.3702 0.1525 −0.3927 0.083 H(7B) 4e 0.4288 0.3000 −0.3652 0.083 H(7A) 4e 0.2632 0.2745 −0.4332 0.083 H(10B) 4e 0.4464 0.3349 0.2710 0.044 H(10A) 4e 0.4666 0.4890 0.2998 0.044 H(11C) 4e 0.4768 0.3969 0.0956 0.044 H(11B) 4e 0.4819 0.5503 0.1251 0.044 H(11A) 4e 0.3685 0.4974 0.0105 0.044 H(1) 4e 0.125(2) 0.374(2) 0.053(2) 0.035 H(4) 4e 0.257(2) 0.762(2) 0.176(2) 0.049 H(5) 4e 0.328(2) 0.460(2) 0.373(2) 0.047 Table 2. Atomic coordinates and displacement parameters (in A). Atom Site x y z Uiso