1,3,2-Dithiazolyls derivatives

There is not one generic route into 1,3,2-dithiazolyl/ium chemistry. For acyclic derivatives the [4+2] cycloaddition chemistry of [SNS][AsF6] to alkynes has been successfully expoited by Passmore.49 Flowever for benzo-fused derivatives, the simplest route is via Wolmershauser s method in which 1,2-sulfenyl... 

Electrochemical studies on a number of derivatives reveal a reversible one-electron reduction to the dithiazolyl radical. The greater spin density at the heterocyclic C atoms in 4 (Figure 1) facilitates greater n-delocalisation onto the fused substituents than observed for 2 and 3. As a consequence the position of the Ei/2 for the +1/0 redox process has been found to be somewhat more... 

However at elevated temperatures (T2 > Tj, Figure 9) the increased entropy (TAS) associated with an open shell structure overcomes the ti —ti enthalpy of dimerisation associated with these distorted Ti-stacked structures and they undergo a solid-solid phase transition (Figure 9) The high temperature phase is typically associated with a Ti-stack of regularly spaced radicals which exhibit longer inter-radical S- S contacts (ca. 3.7 A). This process was first observed by Oakley60 in the DTA radical thiadiazolopyrazine-l,3,2-dithiazolyl 26, and a number of other derivatives have subsequently been identified which exhibit similar behaviour. These are compiled in Table 1. 

Closely related to the 1,3,2-dithiazolyl radicals are the isomeric 1,2,3-dithiazolyl radicals. The benzo-fused derivatives were originally prepared by Herz in 192276 from the reaction of aniline and its derivatives with an excess of S2C12 (Scheme 10). Almost invariably the aromatic ring becomes substituted by chlorine para to the amine N atom. 

Reduction of 38 leads to the formation of the corresponding 1,2,3-dithiazolyl radical. The simple benzo-derivatives have long lifetimes and have been studied extensively by EPR spectroscopy, although attempts to isolate radicals to date appear to have been broadly unsuccessful. The only 1,2,3-dithiazolyl which has been structurally characterised is the non-fused 4-chloro-5-pentafluorophenyl-... 

Only 5 derivatives have been isolated to date. While the non-fused system forms a 71 -ji dimer (<7S s 3.27 A),86 structural studies on the more delocalised derivatives indicate a reduced tendency to dimerise. However, rather than forming optimal n-stacked motifs, there is a clear tendency to adopt slipped n-stack structures which minimise orbital overlap. As a consequence although the Hubbard energy is low, conductivity measurements show poor conductivities (10 5 S cm-1) similar to those observed in either the isomeric 1,3,2-dithiazolyl (4) or 1,2,3,4-dithiadiazolylradicals (2).84... 

Calculations carried out on basis of INDO and GAUSSIAN 76 programs showed the 1,3,2-dithiazolyl cation (1) to have some aromatic character but not sufficient to prevent its easy reduction to the radical (2) the calculated bond lengths and angles agreed well with those derived experimentally by x-ray diffraction <83CC807, 85JCS(D)1405>. 

Figure 3.10 EPR spectra of (a) 1,3,2-dithiazolyl and (b) 1,2,3,5-dithiadiazolyl radicals both absorption and first-derivative spectra are shown.

The biradical benzo-l,2 4,5-bis(l,3,2-dithiazolyl) (BBDTA) is known in the literature but characterization is incomplete. A new study reports the electronic, molecular, and solid-state structure of BBDTA.224 The lifetime of an alkyl phenylglyoxalate-derived 1,4-biradical has been estimated, using the cyclopropylmethyl radical clock , to be in the range 35—40 ns.225 The indanols (88) and their C(3) methyl and trideuteromethyl analogues have been prepared from phenyl benzyl ketone via photo-cyclization of an intermediate 1,5-biradical species.226,227 Selectivity for these products over their C(l) epimers is high but is profoundly effected by substitution in the benzyl ring or the alkyl side-chain. The findings are rationalized in terms of the conformational preference of the intermediate 1,5-biradicals. 

Research in the reviewed period 1995-2005 has covered more the chemistry of 1,3,2-dithiazoles and less the chemistry of 1,3,2-dioxazoles. 1,3,2-Oxathiazoles and their derivatives were not investigated in this period. Much attention has been paid to the neutral 1,3,2-dithiazolyl radicals including their synthesis, theoretical and structural study, and application. Special attention was given to their magnetic properties and conductivity. 1,3,2-Benzodithiazole. Y-oxidcs were of interest as enantiomeric compounds and intermediates for the preparation of enantiopure amines and alcohols. 

The distribution of the total spin density in radicals was calculated using the UB3LYP16-31g method. In systems 1, 3, 4, and 8-11, the spin density is localized on the -S-N-S- fragment with minor spin distribution onto the Jt-framework, presumably through a spin polarization mechanism. For instance, in 1,3,2-dithiazolyl 1, virtually all positive spin density is localized on the -S-N-S- array due to the two polar resonance structures shown in Equation (2). A very similar spin distribution is observed in ring-fused derivatives 3, 4 and 9-11 <2001PCA7615>. 

Benzo-fiised 1,2,3-dithiazolyls 38 are prepared by the reduction of readily prepared Herz salts 37 using decamethylferrocene in acetonitrile (Scheme 8) (1999JA969, 2001CJC1352, 2005IC1837). Se and Te derivatives of fused 1,2,3-dithiazolyls can also be prepared in a similar manner and a wide variety of reductants can be used such as octamethylferrocene, hexamethylferrocene, tetramethyl-p-phenylenediamine, and electrochemical reduction (2008IC10100). 

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