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

The synthesis of the title compounds I 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 Is is obtained as the result of an unexpected 1, not H, substitution. The rate of the I + SCl2 reaction depends upon a substituent 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 multi. nuclear (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 similar to5 degrees and similar to4 degrees, respectively, and the Ir (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 I is interpreted in terms of a pseudo-Jahn-Teller effect as the result of pi -highest occupied molecular orbital (HOMO) - sigma*-(LUMO) lowest unoccupied molecular orbital + I 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 I from 2-aminobenzenethiols and (SN)(4) and from salts 3 and Me3SiN3, and we discuss the reaction pathways. (C) 2001 John Wiley & Sons, Inc.