Dibenzoselenophene

No oxidizing agent is required for the sulfuric acid promoted cyclization of iV,iV-diphenyl-hydroxylamine to carbazole (13CB3304). The parallel conversion of diphenyl sulfoxide and diphenyl selenoxide to dibenzothiophene (23CB2275) and dibenzoselenophene (39CR(199)53l) is effected by treatment with sodamide. 

Dibenzo[6,/][l,4]selenazocine, N-formyl-6,11-dihydro-synthesis, 6, 34l Dibenzoselenophene, 2-amino-diazotization, 4, 951 Dibenzoselenophene, 2-nitro-reduction, 4, 951 Dibenzoselenophene, 3-nitro-5-oxide... 

Both 5e-salt 26 and dinitro 5e-salt 40 gave dibenzoselenophene 5e-oxide 57 and its dinitro derivative 58, respectively (Eq. 16). 

Sawicki, in 1954, deduced the structure of a number of mono- and disubstituted dibenzothiophenes by spectral comparison with known TT-isoelectronio derivatives of carbazole and thereby established the foundations for general structure determination of unknown derivatives of both dibenzothiophene and dibenzoselenophene. - This approach has now been largely replaced by NMR techniques however, general... 

The half-wave reduction potentials (HWP) of dibenzothiophene and some of its derivatives have been measured for comparison with those of dibenzofuran and dibenzoselenophene. A shift to more negative HWP was observed for all of the methyl derivatives studied, the magnitude of which depended on the position of substitution. These shifts are in accord with LCAO molecular orbital theory predictions if the sulfur d orbitals are excluded from the calculations (Section III, A). ... 

Three derivatives of 3-aminodibenzothiophene, 110a, 110b, and 110c, have been nitrated, and in each case substitution occurred in the 4-position. Hydrolysis of the products yielded 3-amino-4-nitro-dibenzothiophene, which was different from the previous two nitro-amines and which formed an imidazole different from both 104 and 109. Deamination of this nitroamine via diazotization gave a small amount of 4-nitrodibenzothiophene. An alternative synthesis of the 4-nitro compound is described later. The spectroscopic techniques used above by Sawicki were later extended to determine the positions of substitution in dibenzoselenophene, in this case by comparison with the above-established derivatives of dibenzothiophene. - ... 

Sulfuric acid promotes cyclization of (V./V-diphenylhydroxylamine (14) to carbazole (11) (13CB3306). The parallel conversions of diphenyl sulfoxide (15) and diphenyl selenoxide to dibenzothiophene (10) (23CB2275) and dibenzoselenophene (39CR(i99)53i) are effected by sodamide. 

The numbering system used for selenophene (1), tellurophene (2), benzo[6]selenophene (3) and benzo[6]tellurophene (4) is shown in Figure 1. Positions 2 and 5 in selenophene and tellurophene are referred to as a-positions and positions 3 and 4 are termed /3-positions. Alternative names for tetrahydroselenophene and tetrahydrotellurophene are selenolan and tellurolan, respectively. Benzo[c]selenophene (5), dibenzoselenophene (6) and diben-zotellurophene (7) are numbered as shown. The C4H3Se radicals (8) and (10) derived from selenophene are named 2-selenienyl and 3-selenienyl the corresponding tellurium species are named 2-tellurienyl (9) and 3-tellurienyl (11). 

Benzo[6]tellurophene has also been found to form 1,1-addition compounds with halogens and with methyl bromide (73BSF2468). Both dibenzoselenophene (68LA(715)68) and diben-zotellurophene (68LA(712)l) are converted to the corresponding 5-(p-toluenesuIfonylimine) derivatives by chloramine-T. 

Selenophene is reported to be little affected by oxidizing agents under mild conditions (B-79MI31600) and tellurophene is reported to be fairly stable to light and air at room temperature <77AHC(2l)ii9). Dibenzoselenophene forms a 5-oxide when treated with peracetic add in acetic acid, a compound also obtained when the 5,5-dibromide is reacted with dilute aqueous sodium hydroxide (50JA5753). 

Dibenzoselenophene has been obtained by the sodamide promoted cyclization of diphenyl selenoxide (153) (34CR(l99)53l), and via diazotization of o-aminodiphenyl selenide (154) (39JCS151). 

The cyclization of the benzo[f>]selenophene derivative (241) provides a useful source dibenzoselenophene-1-carboxylic acid (242) <73CR(C)(277)383). 

Dibenzoselenophene is readily alkylated to the selenienyl salts (62), which are powerful methylation and trifluoromethylation agents [98, 99], Halogens preferentially attack a-carbon in selenophenes but the 1,2-dibromo-l-benzoselenophenium bromide (63) was found among the bromination products of 1-benzoselenophene (Fig. 6) [100],... 

By far the most common methods for the preparation of dibenzoselenophenes and 2-benzoselenophenes, like the synthesis of 1-benzoselenophenes, rely upon the annulation of the heterocyclic ring system onto a preformed benzene ring and mostly involve the formation of one or two Se-C bonds as their key steps, with only a few exceptions [1, 119, 120], Intramolecular electrophilic aromatic substitution of biphenyl-2-yl trifluoromethylselenide to 5-(trifluoromethyl)dibenzoselenopheni um triflate (62) [99, 143] and synthesis of tetramethoxydibenzoselenophene (95) (Scheme 26) [144, 145] are examples. 

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