2,1,3-Benzoselenadiazoles

A preparative route to 4,5-benzo-l,3-diselenol-2-selones (63) is based on the ready decomposition of benzoselenadiazoles (62) in boiling carbon diselenide (Equation (6)) <83CC295>. Thermal and photochemical decomposition of 1,2,3-benzoselenadiazole gave successively benzoseleniren (64) and 6-fulveneselone (65) as very reactive products <80AG(E)69,83ZN(B)611,84TL2337> (Scheme 2). 

In the variable temperature photoelectron spectroscopy of 1,2,3-selenadiazole (101) at 5 x 1(T2 mbar between 450 and 750 °C, acetylene is always formed along with selenoketene (105). At 800 °C, acetylene is the sole product. 1,2,3-Benzoselenadiazole (106) does not produce benzyne even at 800 °C. The reaction product was found to be the highly reactive 6-fulveneselone (107). The PE spectra of (101), (106) and their decomposition products are very similar to those of their corresponding sulfur analogs (Scheme 45) (80CB3187)... 

Base-catalyzed reaction of selenadiazole (161) with acid chlorides affords tricyclic selenadiazoles (162 Scheme 64) (78CB3423). 1,2,3-Benzoselenadiazole (106) and its 4- and 5-methyl derivatives reported by Keimatsu and Satoda in 1935 (35YZ233) are prepared by the reaction of nitrous acid and 2-aminobenzeneselenols (Scheme 65). 

Elimination of nitrogen by irradiation of argon matrix-isolated 4,5-bis(methoxycarbonyl)-l,2,3-thiadiazole (38) resulted in the almost quantitative formation of bis(methoxycarbonyl)thiirene (39), confirming earlier predictions that electron-withdrawing substituents should stabilize the thiirene ring. Benzoselenirene (40) has similarly been obtained and identified spectroscopically on irradiation of matrix-isolated 1,2,3-benzoselenadiazole (41) rearrangement to the fulveneselone (42) is observed on further irradiation. 

As mentioned in Section 1.07.3(b), irradiation (254 nm, 4 min) of 1,2,3-selenadiazole (27) in argon matrix produced a reactive intermediate benzoselenirene (28) (see Equation (6)), the formation of which was confirmed by IR spectra. The matrix-isolated benzoselenirene (28) undergoes ready rearrangement to 6-fulveneselone (29) on further irradiation (Equation (8)). Benzoselenirene (28) is also formed in gas-phase pyrolysis (560°C, ca. I03 min) of 1,2,3-benzoselenadiazole (27) if the reaction temperature is kept a little lower than required for complete fragmentation of (27). Selenirene (28) was found to undergo thermal rearrangement to (29), the IR spectrum of which is identical with that obtained in the exhaustive photolysis of (27). With increasing temperature, the amount of the new product steadily decreased and at 700°C its IR bands were at the limit of detection. 

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). 

Thermolysis of 1,2,3-selenadiazole affords only selenoketen (144) and acetylene above 800 °C, acetylene is the only organic product. Thermolysis of 1,2,3-benzoselenadiazole (145) yields the fulvaselone (146), which was observed as an unstable red deposit on a cold finger at —196 C it was identified by p.e. spectroscopy. ... 

A number of 1,2,3-benzoselenadiazoles were quaternized successfuUy with alkyl 2,4-dinitrobenzenesulphonates in nitrobenzene. The reactivity... 

Schulz, R. and Schweig, A., Photolysis and gas phase pyrolysis of 1,2,3-benzoselenadiazole matrix isolation of benzoselenirene. Tetrahedron Lett., 25, 2337, 1984. 

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