Substituted 1,3,2,4‐benzodithiadiazines and related compounds

Despite some limitations, the 1:1 condensation of n‐RC₆H₄‐N=S=N‐SiMe₃ (n = 2, 3, 4; R = CH₃, OCH₃, F, Cl, CF₃) with SCl₂, followed by intramolecular electrophilic ortho‐cyclization, was found to be a general synthetic approach to the corresponding 5‐R, 6‐R, and 7‐R–substituted 1,3,2,4‐benzodithiadiazines, formally antiaromatic 12π‐electron compounds. For precursors with n = 3, the high regioselectivity of the cyclization resulted in exclusive (R = OCH₃, F) or predominant (R = CH₃, Cl) formation of 6‐R isomers; the ratio of the major 6‐R isomer to the minor 8‐R one was found to be 72:28 (R = CH₃) or 78:22 (R = Cl). The preferred direction of cyclization is consistent with thermodynamics of the corresponding intermediate σ‐complexes as well as factors of kinetic control for an orbital‐controlled El‐Nu reaction. According to the X‐ray diffraction data, the molecules of 5‐CF₃ (15) and 6‐F (12) derivatives are nearly planar, while the molecules of 5‐OCH₃ (7) and 6‐CH₃ (4) derivatives are bent along the S¹ … N⁴ line by ～11° (7) or 7° (4). An attempt to adopt CsF‐induced intramolecular nucleophilic ortho‐cyclization of Ar_F‐S‐N=S=N‐SiMe₃ into polyfluorinated 1,3,2,4‐benzodithiadiazines for polyfluoropyridine derivatives resulted in formation of polyfluorinated aminopyridines. Data obtained are consistent with a previously suggested scheme of sulfur–nitrogen chain shortening during cyclization. Mild acid hydrolysis of the title compounds was shown to be a convenient synthetic route to substituted 2,2′‐diaminodiphenyl disulfides (including polyfluorinated ones) via the corresponding 2‐aminobenzenethiols. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 113–124, 1999