Fluorinated 1,3λ⁴δ²,2,4‐Benzodithiadiazines − A Synthetic, Structural and Theoretical Study

Abstract

The series of title compounds has been prepared through both electrophilic (C6HnF5−n−N=S=N−SiMe3 + SCl2) and nucleophilic (C6HF4−S−N=S=N−SiMe3 + CsF) intramolecular ortho‐cyclisation reactions, and the former route seems to be the more effective. High regioselectivity of the ring‐closing procedures is observed in both cases. The compounds were characterised by X‐ray crystallography and multinuclear (1H, 13C, 15N and 19F) NMR spectroscopy. In accordance with GIAO calculations, 15N{1H} experiments and the effects observed on complete substitution of hydrogen by fluorine, the high‐field signal in the 15N NMR spectra can be assigned to N‐4 and the low‐field signal to N‐2. In the crystal, 5,6,7‐trifluoro‐ (5) and 5,6,8‐trifluoro‐1,3λ4δ2,2,4‐benzodithiadiazine (6) are planar, whereas the 6,8‐difluoro derivative 3 is bent along the S1···N4 line by 8.3°. According to NICS calculations the heterocycle moiety in this compound class is antiaromatic while the carbocycle is aromatic. The fluorine substituents increase the aromaticity − and in some cases (especially when a fluorine atom is present in the 8‐position) the antiaromaticity − of the corresponding rings. The ortho‐fluoro‐containing starting material C6HnF5−n−N=S=N−SiMe3 (n = 2: 10) cyclises to the fluorinated 2,1,3‐benzothiadiazole 27 upon treatment with CsF instead of SCl2. For starting compound 6‐HC6F4−S−N=S=N−SiMe3 (14) the planar (Z,E) configuration features a short intramolecular H···N contact, as evidenced by X‐ray diffraction. Both the reaction pathways mentioned are also discussed. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

Roesky’s Ketone: Structure, Aromaticity and Reactivity

“…For a benzene ring as the closing fragment it was found in the gas‐phase electron diffraction (GED) study5 of 1,3λ 2 δ 4 ,2,4‐benzodithiadiazine that the heterocycle features one localized single S−N bond [1.697(5) Å] and two localized S=N double bonds [1.548(3) and 1.543(3) Å]; this trend was confirmed by a B3LYP/6‐311+G* calculation yielding 1.717, 1.570 and 1.566 Å as the bond lengths, respectively. This geometrical data, together with a calculated NICS value of 14.99 ppm at the B3LYP/6‐31+G* level,6 indicates that the heterocyclic ring is anti‐aromatic; a positive value indicates anti‐aromaticity, a value approximating zero nonaromaticity and a negative value aromaticity. For 5‐oxo‐1,3,2,4‐dithiadiazole ( 1 ), where the ring is closed by a carbonyl group, we find more intermediate bond lengths of 1.641, 1.608 and 1.595 Å, which suggest a higher degree of electron delocalisation and thus a higher degree of aromaticity.…”

On the Usefulness of Bond Orders and Overlap Populations to Chalcogen–Nitrogen Systems

“…Consequently, it is logical to investigate their performance for more exotic systems, in particular compounds 1-4, which are of special interest to our research. [3][4][5][6] First, a number of simple compounds which contain formal single, double and triple NS and NSe bonds were studied. The results are given in Table 4.…”

“…In our earlier work we have dealt with various compounds containing an (SN) 2 fragment such as 1,3λ 4 δ 2 ,2,4-benzodithiadiazine (1), [3] its fluorinated derivatives [4] and Roesky's ketone (4). [5] 3λ 4 δ 2 ,1,2,4-Benzothiaselenadiazine (2) and 1,3λ 4 δ 2 ,2,4-benzodiselenadiazine (3), the mono-and diselena analogues of 1, are also of considerable interest and are presently targets for synthesis.…”

Effects of different GIAO and CSGT models and basis sets on 2-aryl-1,3,4-oxadiazole derivatives

“…?G(d,p) basis sets and HF method with 6-31G? (d) basis set [42,43]. These calculations are not sufficient in our study.…”