Title
Fluorinated <tex>$1,3\lambda^{4}\delta^{2},2,4$</tex>-benzodithiadiazines : a synthetic, structural and theoretical study Fluorinated <tex>$1,3\lambda^{4}\delta^{2},2,4$</tex>-benzodithiadiazines : a synthetic, structural and theoretical study
Author
Faculty/Department
Faculty of Sciences. Chemistry
Publication type
article
Publication
Weinheim ,
Subject
Chemistry
Source (journal)
European journal of inorganic chemistry. - Weinheim
Volume/pages
(2003) :1 , p. 77-88
ISSN
1434-1948
ISI
000180388900013
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
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 (H-1, C-13, N-15 and F-19) NMR spectroscopy. In accordance with GIAO calculations, N-15{H-1} experiments and the effects observed on complete substitution of hydrogen by fluorine, the high-field signal in the N-15 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-1,3lambda(4)delta(2),2,4-benzodithiadiazine (6) are planar, whereas the 6,8-difluoro derivative 3 is bent along the S1...N4 line by 8.3degrees. 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. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003).
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