Eight- and 16-Membered Cyanuric−Sulfanuric Ring Systems: C₂N₄S₂ → C₂N₃S Ring Contraction

Eight- and 16-membered cyanuric−sulfanuric ring systems of the type Ar2C2N4S2(O)2Ar‘2 (3a, Ar = 4-BrC6H4, Ar‘ = Ph; 3b, Ar = 4-CF3C6H4, Ar‘ = Ph; 3c, Ar = 4-CF3C6H4, Ar‘ = 4-CH3C6H4) and Ar4C4N8S4(O)4Ar‘4 (4b, Ar = 4-CF3C6H4, Ar‘ = Ph; 4c, Ar = 4-CH3C6H4, Ar‘ = Ph; 4d, Ar = 4-CF3C6H4, Ar‘ = 4-CH3C6H4), respectively, were prepared in good yields by the reaction of the corresponding sulfur(IV) systems with m-chloroperbenzoic acid. The X-ray structures of 3b, 3c·C7H14, 4b·CH2Cl2, 4c, and the S(IV) system Ar4C4N8S4Ar‘4 (2c, Ar = 4-CH3C6H4, Ar‘ = Ph) were determined. Upon oxidation the two oxygen atoms in 3b and 3c·C7H14 adopt endo positions leading to a twist boat conformation for the C2N4S2 ring. The 16-membered C4N8S4 rings in 4b and 4c retain a cradle conformation upon oxidation. The S−N bond distances are ca. 0.06 Å shorter in all the S(VI) systems compared to those in the corresponding S(IV) rings. The thermolysis of 3b at ca. 220 °C occurs primarily via loss of a sulfanuric group, NS(O)Ph, to give the six-membered ring (4-CF3C6H4)2C2N3S(O)Ph (6). The structure of 6 was confirmed by X-ray crystallography. Crystal data: 2c, triclinic, space group P1̄ with a = 13.917(2) Å, b = 15.610(4) Å, c = 13.491(3) Å, α = 95.77(2)°, β = 114.82(1)°, γ = 76.21(2)°, V = 2583(1) Å3, and Z = 2; 3b, monoclinic, space group P21/a with a = 7.316(2) Å, b = 29.508(5) Å, c = 12.910(2) Å, β = 101.30(2)°, V = 2733(1) Å3, and Z = 4; 3c·C7H14, triclinic, space group P1̄ with a = 12.849(4) Å, b = 12.863(4) Å, c = 12.610(7) Å, α = 110.61(3)°, β = 105.77(3)°, γ = 62.77(2)°, V = 1719(1) Å3, and Z = 2; 4b·CH2Cl2, triclinic, space group P1̄ with a = 12.647(3) Å, b = 19.137(3) Å, c = 12.550(2) Å, α = 105.765(11)°, β = 93.610(15)°, γ = 88.877(16)°, V = 2917.2(9) Å3, and Z = 2; 4c, orthorhombic, space group Pba2 with a = 22.657(2) Å, b = 10.570(2) Å, c = 10.664(3) Å, α = β = γ = 90°, V = 2554(1) Å3, and Z = 2; 6, triclinic, space group P1̄ with a = 7.4667(8) Å, b = 11.3406(12) Å, c = 13.5470(14) Å, α = 108.000(2)°, β = 105.796(2)°, γ = 94.300(2)°, V = 1033.8(2) Å3, and Z = 2.