1.2.5.6- tetrathiocins

Tetrathiocine 3 was first synthesized in 1996 <1996AGE2357> (see Equation (28) in Section 14.09.9.1.2). Among several conformers optimized for 3 at local minima by ab initio (MP2/D95 ), the twist boat form 4 was calculated to lie on the lowest potential level. The calculations indicate that the energy difference between the two... 

A weak Ss" peak was observed in the electron impact mass spectrum of the 1,2,5,6-tetrathiocine 21 indicating the absence of polysulfide linkages (see Scheme 4 in Section 14.09.10) <1994IC4537>. Formation of the mixed oxidation state [S(iv) and S(vi)] heterocycle 22 has been confirmed by a strong molecular ion in the electron impact mass spectrum <2000IC1697>. 

The ultraviolet spectra of 1,2,5,6-tetrathiocines 23 (Amax 350nm, e 7500) and 24 (Amax 361 nm, e 36000) were helpful in the comparison of their photochemical reactivity (see Section 14.09.5) <2002BCJ2647>. 

X-Ray crystallography has confirmed the existence of 1,2,5,6-tetrathiocine 3 as the twisted conformer 4 (see Section 14.09.2) <1996AGE2357>. The fluoro-substituted dibenzo-l,2,5,6-tetrathiocine 6 (X = F) adopts the chair conformation 8 in the crystalline state, while the chloro compound 6 (X = Cl) was found in the twist boat conformation 7 in solid state (see Section 14.09.2) <1998CJC1093>. The calculated difference in the energies of the two conformers 7 and 8 for the fluoro-substituted derivative 6 is very small (<5 kj mol-1), and its slow conformational isomerization in solution was... 

Irradiation of the 1,2,5,6-tetrathiocine 24 in CH2C12 at room temperature resulted in the mixture of two products, the dithianthrene 25 and trithiepine 26 (Equation 3) <2000TL1801, 2002BCJ2647>. In turn, the trithiepine 26 can be further desulfurized on irradiation to give the dithianthrene 25. 

The Hg2+-promoted hydrolysis of the thiocarbonyl groups was accompanied with an unexpected ring rearrangement in the 1,2,5,6-tetrathiocine 21 (Section 14.09.3.2) and produced the 1,2,3,6-tetrathiocine 20 (Section 14.09.3.1) (Equation 6) <1994IC4537>. 

Photolysis of the 1,2,5,6-tetrathiocine 31 promoted a reversible, transannular sulfur migration to give 1,2,3,6-tetrathiocine 32 (Equation 7) <1998CJC1093>. The photoisomerized product 32 was readily distinguished by the 19F NMR spectrum, which exhibits an AMXY pattern. 

Since 1,2,5,6-tetrathiocine 3 (see Sections 14.09.2 and 14.09.9.1.2) is unstable toward irradiation and even room light, upon irradiation in a benzene solution, the thiocine 3 formed the bicyclic compound 33 in low yield together with a polymer, as the main product (Equation 8) <1996AGE2357>. Irradiation of 3 in the presence of a large excess of 2,3-dimethylbutadiene hindered the formation of the polymer, and the bicyclic product 34 was obtained together with a small amount of the symmetrical bicycle 33 (Scheme 1) <1996AGE2357>. This indicates the formation of the intermediate thioaldehyde 35 by photochemical rearrangement of thiocine 3, while several mechanisms are plausible for the formation of the symmetrical 33. 

In the study of the controlled elimination of one sulfur atom from the trithiols 112 to generate the benzo-dithietes 113, the 1,2,5,6-tetrathiocines 115 were isolated in high yield (Scheme 8) <1995T2533>. It was suggested that the equilibrium between the benzothiete 113 and o-dithiobenzoquinone 114 should favor dimerization to form 115. 

Dithiastannole 117 was coupled oxidatively into the sterically hindered 1,2,5,6-tetrathiocine 27 in good yield (Equation (37) see Equation (4) in Section 14.09.5) <1999TL9101>. 

The first example of an enzymatic cleavage of trithiocarbonate 127 followed by oxidative dimerization was reported to give an inseparable mixture of 1,2,5,6-tetrathiocines 128 and 129 (Equation 40) <2002TL2589>, whose structure assignments were based on mass spectrometry data. 

Without additional reagents 1,2,5,6-Tetrathiocins from 1,2-dithietenes... 

Tetrathiocins via 1,2-dithietenes. A flask containing sulfur purged with Ng while the sulfur is heated to reflux, then Ng shut off and hexafluoro-2-butyne passed in during 20 min. while the product is continually withdrawn 3,4-bis (trifluoromethyl)-1,2-dithietene (Y 80%) stored 2 months at 25°... 

---