2.1.3- Benzoselenadiazole

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)... 

Benzoselenadiazole (bsd) has been used as a ligand in the ruthenium complex [RuClH-(CO)(bsd)(PPh3)2]. This complex was used to catalyse the transalkynylation and catalytic demercuration of bis(alkynyl)mercurials <96CC1059>. 

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-... 

Copper(ii) complexes of isothiazole, 2,1,3-benzoselenadiazole and 2,1,3-benzothiazole, thiophenealdoxime, and morpholine-4-carbodithioate have been reported. Thiodiethanol, ethylenedithiodiacetate, and diethylene-trithiodiacetate all form 1 1 complexes with... 

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>. 

Table 3 Bond lengths (A) and bond angles (°) in 2,1,3-benzoselenadiazole (1).

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). 

Benzoselenadiazole (1) is alkylated by dialkyl sulfates and dialkyl 2,4-dinitrobenzene sulfonates to give 1-alkyl 2,1,3-benzoselenadiazolium salts <89SC1381>. 2,1,3-Benzoselenadiazole (1) reacts with I2, KI and HCl in CHCI3 to give the quasi-polymeric structure (9) <85ZAAC(523)33> (see Section 4.21.3.1). 

Reaction of o-phenylenediamines with Se(IV) reagents continues to be the method of choice for the synthesis of 2,1,3-benzoselenadiazoles. Selenium dioxide is commonly used <84HCA574,... 

The preparation of quinoxaline derivatives carrying a substituent in the benzene ring requires suitably substituted o-phenylenediamines. These have been prepared by reductive cleavage (SnCl2) of appropriately substituted 2,1,3-benzoselenadiazoles (I9).21 Benzo-selenadiazoles, readily prepared from 1,2-diaminobenzenes and selenium dioxide, undergo halogenation at positions 4 and 7 and sulfonation at C-4. 5,6-Dichloro- 2,3-diphenylquinoxaline has been synthesized from benzil and l,2-diamino-3,4-dichlorobenzene, the diamine in turn was obtained from 4,5-dichloro-2,l,3-benzoselenadiazole.22... 

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