Substituted 1,3,2,4‐benzodithiadiazines: Novel derivatives,by‐products,and intermediates*

The synthesis of the title compounds 1 by 1 : 1 condensation of Ar NSNSiMe₃ 2 with SCl₂ followed by intramolecular ortho‐cyclization of each Ar NSN S Cl] intermediate is complicated by further reaction of 1 with SCl₂ to give Herz salts 3 . With the 2 :SCl₂ ratio of 2:1, the formation of by‐products 3 is reduced and novel compounds 1 are accessible. With ortho‐I containing starting material 2j , the parent compound 1s is obtained as the result of an unexpected I, not H, substitution. The rate of the 1 + SCl₂ reaction depends upon a substituent's position, and the minor 8‐R isomers 1l,p (R = Br, I) are isolated for the first time from mixtures with the major 6‐R isomers due to reduced reactivity toward SCl₂. The synthesized compounds 1–3 are characterized by multinuclear (including nitrogen) NMR and X‐ray crystallography. According to the X‐ray diffraction data, 1j (6‐Br) and 1k (7‐Br) derivatives are planar, whereas 1i (5‐Br) and 1l (8‐Br) are bent along the S1···N4 line by ∼5° and ∼4°, respectively, and the 1r (7‐OCH₃) derivative is planar in contrast to the known 5‐OCH₃ isomer, which possesses a significantly folded heterocycle. The distortion of the planar geometry of some compounds 1 is interpreted in terms of a pseudo‐Jahn‐Teller effect as the result of π‐highest occupied molecular orbital (HOMO)  σ*‐(LUMO) lowest unoccupied molecular orbital + 1 mixing in a planar conformation. The 2p compound is the first structurally defined Ar–N = S = N–SiMe₃ azathiene. The compound Ar–N = S = N–S–NH‐Ar 6 modeling the aforementioned intermediate has been isolated and structurally characterized. We describe the attempts to synthesize compounds 1 from 2‐aminobenzenethiols and (SN)₄ and from salts 3 and Me₃SiN₃, and we discuss the reaction pathways. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:563–576, 2001