The title compound -(N-protected amino)--lactam (C36H33N2O5ClS), derivative of 1,5-benzothiazepine, was prepared by the reaction of 1,5-benzothiazepine 1 with (4R)- phenyloxazolidylacetyl chloride and characteized by X-ray diffraction analysis. The title compound crystallizes in orthorhombic system, space group P212121 with a=12.293(2), b=26.026(5), c=10.146(2)? V=3246.1?, Z=4, Dc=1.312g/cm3, Mr=641.15, F(000)=1344, μ= 0.228 mm1. The final R=0.0597 and wR=0.1165 for 3226 observed reflections with I ≥ 2?I). The crystal structure shows that the 4-phenyloxazolidyl and phenyl attached to C(8) and C(9) are in cis positions, and no trans product was discovered. So the cyclization to -lactam is stereospecific. The title compound - (N-protected amino) -lactam (C36H33N2O5ClS), derivative of 1,5-benzothiazepine, was prepared by the reaction of 1,5-benzothiazepine 1 with (4R) -phenyloxazolidylacetyl chloride and charactetized by X-ray diffraction analysis. The title compound crystallizes in orthorhombic system, space group P212121 with a = 12.293 (2), b = 26.026 (5), c = 10.146 (2)? V = 3246.1 ?, Z = 4, Dc = 1.312 g / cm3, Mr = 641.15, F (000) = 1344, μ = 0.228 mm1. The final R = 0.0597 and wR = 0.1165 for 3226 observed reflections with I ≥ 2? I). The crystal structure shows that the 4-phenyloxazolidyl and phenyl attached to C (8) and C (9) are in cis positions, and no trans product was discovered. So the cyclization to -lactam is stereospecific.