Transannular sulfur-nitrogen interaction in 1,5-thiazocine derivatives: An x-ray study

Article abstract of DOI:10.1016/0022-2860(96)09237-X

7-Acetylbenzo[b]naphtho[1,8-f,g]thiazocin-8(7H)-one(sulfide- N- acetyllactam 3) and its 13-oxide (sulfoxide-N-acetyllactam 4, exhibiting polymorphy, 4a and 4b) have been prepared and their structures established by X-ray crystallography from diffractometer data. Compound 3 (C₁₉H₁₃NO₂S) crystallizes in the monoclinic space group P2₁/c with a = 10.716(3), b = 9.222(2), c= 16.077(5) A,β = 106.68(2)°, V = 1521.9(7) A, Z = 4, D(c) = 1.394g cm^-3 and μ(Mo Kα) = 0.22 mm^-1. Compound 4a (C₁₉H₁₃No₃S) crystallizes in the monoclinic space group Pc with a 7.821(1), b = 24.795(6), c = 8.342(1) A,β = 101.15(1)°, V = 1587.2(4) A³, Z = 4 (two molecules, 4a' and 4a_, in the asymmetric unit), D(c) = 1.40 g cm^-3 and μ(Mo Kα) = 0.21 mm^-1. Compound 4b also crystallizes in the monoclinic space group P2₁/c with a = 11.791(1),b = 10.719(1),c = 25.193(2) A,β = 96.02(1)°, V = 3166.4(4) A₃, Z = 8 (two molecules, 4b' and 4b' in the asymmetric unit), D(c) = 1.394 g cm^-3 and μ(Cu Kα) = 1.92 mm^-1. The crystal structures were solved by direct methods and refined to R = 0.052 for 3, R = 0.088 for 4a, and R = 0.048 for 4b, by using 9413, 4759 and 5195 reflections, respectively. Owing to the cis-amide structure, compounds 3 and 4 assume a boat-like conformation with transannular sulfur- nitrogen close contact; r(S ··· N) = 2.968(1) A for 3 and 2.753(3)- 2.832(2) A for 4a' and 4b_. The out-of-ring position of the sulfinyl oxygen leads to a sulfurane-like trigonal bipyramidal geometry about sulfur in 4a' and 4b'; Θ(O = S ··· N) = 175.8(3)178.7(2)°. The interatomic distances r(S = O) = 1.483(2) 1.498(3) A and r(O=S ··· N) = 4.245 4.314 A are in agreement with an S=O double bond and S ··· N close contact rather than with an O S N type molecular structure observed in spirosulfuranes. The stereochemistries of 1,5-thiazocine and 1,5-thiazonine rings are compared.