Benzothiadiazoles and 2,1,3-Benzoselenadiazoles

3-Benzothiadiazoles and 2,1,3-Benzoselenadiazoles. - Biologically active substances among benzo-2,l,3-thiadiazole derivatives have been reviewed, with 83 references. The synthesis of 4-bromobenzo-2,l,3-thiadiazole-7- 

Belen kaya and G. P. Krokhina, Deposited Document, 1980, VINITI 3843 — 80 Chem. Abstr., 1982, 96, 68 851). 

CH2CHNH2CO2H] The complexes were characterized by i.r., u.v., and n.m.r. spectra. The ground- and excited-state configurations of the electrons of 4-substituted benzothiadiazoles (295 X = S R = H, NH2, or OH) were calculated the 7r-/a-bonds, total energies, and heats of atomization of (295), their protonated forms, and their tautomers were tabulated. The hydroxy-and amino-tautomers are more stable than the 0x0- and imino-tautomers, respectively. Compounds (295) are protonated on N-1. The linear dichroism and m.c.d. spectra of 2,1,3-benzothiadiazole and 2,1,3-benzo-selenadiazole were measured and c.d. spectra reported for the j3-cyclodextrin compound with the heterocycle. The kinetics of formation and equilibrium data have been reported for the Meisenheimer complexes of the benzothia- and benzoselena-diazoles (295 X = S, or Se R = 4-NO2) with MeO in MeOH/DMSO.  

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The syntheses from [4 + 1] atom fragments, in which the Group VIA heteroatom is introduced between two nitrogen atoms, are the most widely applicable and versatile methods available for construction of the 1,2,5-thiadiazole and 1,2,5-selenadiazole ring systems. These methods have been applied to the synthesis of monocyclic and polycyclic aromatic forms of these ring systems in addition to the direct formation of 1-oxides and 1,1-dioxides, 2-oxides, quaternary salts and reduced forms. The earliest use of the [4 + 1] synthesis dates back to 1889 when Hinsburg prepared 2,1,3-benzothiadiazole (1) and 2,1,3-benzoselenadiazole (2) from o-phenylenediamine and sodium bisulfite, or selenium dioxide, respectively. 

The ring system has been the subject of quantum-chemical calculations. The outstanding feature of the mass spectra of the 2,1,3-benzothiadiazoles (35 examples) is the occurrence of molecular ions of very great abundance. Fragmentations analogous to the benzyne formation postulated in the case of the 2,1,3-benzoselenadiazoles are not encountered. The polarographic behaviour of a large number of 2,1,3-benzothiadiazoles, of 2,1,3-benzoselenadiazole, and of several fused 1,2,5-thiadiazoles has been examined. ... 

Although derivatives of 2,1,3-benzoxadiazole have been used extensively to make quinoxalines (see Section 1.6.7), the corresponding selena and thia systems have been paid scant attention for that purpose. However, 5-chloro-4-nitro-2,l,3-benzoselenadiazole (456) has been used as a convenient source of 4-chloro-3-nitro-1,2-benzenediamine (457) (HCl + HI, 20°C, 2 h 88%), which was then converted into 6-chloro-5-nitro-2,3(l//,4//)-quinoxalinedione (458) (oxalic acid, 2M HCl, reflux, 2.5 h 23%). ° In addition, irradiation of 2,1,3-benzoselenadiazole (460, X = Se) or 2,1,3-benzothiadiazole (460, X = S) with dimethyl acetylenedicarboxy-late afforded, among other products, dimethyl 2,3-quinoxalinedicarboxylate (459)... 

In 2-heterosubstituted benzo derivatives (Scheme 51), the effect of the heteroatom X on the ring is similar to the azole series above, and the decreasing scale of aromaticity is 2,1,3-benzoselenadiazole (118)-> 2,1,3-benzothiadiazole (119) > 2,1,3-benzoxadiazole (120).111... 

The product of the reaction between bis(S-aminodithionitrito)nickel(ii), NH3, HCHO, and MeOH has the structure (179). Complexes of 2,1,3-benzothiadiazole, 2,1,3-benzoselenadiazole, isothiazole, 2-methylbenzo-... 

The C NMR chemical shifts and one-bond coupling constants J( C—H) have been obtained for 2,1,3-benzothiadiazole, 2,1,3-benzoselenadiazole, and 2,1,3-benzooxadiazole in carbon disulfide <74OMR(6)430>. 

The photoelectron spectrum of 2,1,3-benzoselenadiazole (1), 2,1,3-benzothiadiazole and their tetrafluoro derivatives were measured. Replacement of sulfur by selenium did not appreciably alter the 7t molecular-orbital ionization energies <91KGS563). 

Photolysis of 2,1,3-benzothiadiazole 1-oxide produces l,3-dihydro-2,l,3-benzothia-diazole 2,2-dioxide, shown by flash photolysis to be formed via hydration of the 2-oxide intermediate <78ACS(B)625). Independent of this process 2-thionitrosobenzene is generated reversibly as a short-lived intermediate, analogous to the thermal and photochemical formation of a 1,2-dinitroso intermediate from benzofuroxans. Preliminary flash photolysis and spectrometric results point to a nitroselenanitroso pathway in the photolysis of 2,1,3-benzoselenadiazole 2-oxide to benzofurazan (76ACS(B)675>. 

Benzoselenadiazole (128) behaves as a heterodiene toward dimethyl acetylenedicarboxylate, with which it gives the quinoxaline 124 and selenium. But 128 reacts differently with benzyne (generated from 4 or from 9) to give the 1,2-benzisoselenazole derivative 132 (88%) and a small amount of a cis,trans stereoisomer of 132.82 The analogous adduct 131 is obtained in lower yield from benzyne and 2,1,3-benzothiadiazole (127). The structure of these benzyne adducts is strikingly reminiscent of 135, which is obtained from a photochemical addition of dimethyl acetylenedicarboxylate to 126 via a nitrile oxide intermediate.84 However, for reasons given elsewhere,82 a nitrile selenide is unlikely to be an intermediate in the formation of 132, which is better explained by the mechanism outlined in Scheme 16. As in the case of thiophen (Section V,B), this is a 1,3-cycloaddition (in one or two steps) of benzyne to the heterocycle, enabled by the use of d orbitals on the sulfur or selenium atom. 

Stufkens has reviewed the photochemistry and photophysics of zerovalent (f complexes of diimine ligands luminescence is observed from [(CO)4M(LL)] (M = Mo , W and LL = diimine). Other examples of zerovalent d complexes exhibiting MLCT emission include the bimetallic complexes (/x.-bpym) Mo(CO)4]2, which exhibits weak emission with an onset at 700 nm in CH2CI2. and [W(C0)5]2L (L = 2,l,3-benzothiadiazole, 2,1, 3-benzoselenadiazole) that shows weak near-IR (>750 mn) MLCT emission... 

A low band gap copolymer consists of poly(2,7-(9,9-dioctyl)fiuorene-co-5,5 -(4,7-diselenophenyl)-2,2 -yl-2,l,3-benzothiadiazole). The optical band gap of this type of copolymer is very low, e.g., 1.87 eV for a copolymer obtained from substituted fluorene and 4,7-diselenophen-2 -yl-2,1,3-benzothiadiazole, and 1.77 eV for a similar copolymer from 4,7-dise-lenophen-2 -yl-2,l,3-benzoselenadiazole. The efficient fast energy transfer from fluorene segments to narrow band gap sites was observed. 

The thermal and photochemical behavior of benzoselenirene (28) derived from 1,2,3-benzoselenadiazole (27) is very similar to that of benzothiirene (28) generated by the thermolysis or photolysis of the 1,2,3-benzothiadiazole (30) (78JOC2490, 83ZN(B)6li>. Thus, benzothiirene (31) was also found to undergo thermal or photochemical rearrangement to the corresponding 6-ful-venethione (32) (Scheme 3). 

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