Benzo 6 selenophene acylation

Benzoselenolo[2,3-ii]benzoselenophenes synthesis, 4, 116, 1078 Benzoselenolopyrylium cations oxidative ring contraction, 4, 969 [l]Benzoselenolo[3,4-ii][l,2,3]selenadiazoles synthesis, 6, 354 Benzo[h]selenophene, 2-acetyl-synthesis, 4, 966 Benzo[h]selenophene, 2-bromo-acylation, 4, 948... 

Acetylbenzo[6]tellurophene is also formed in isolable quantities. Benzo[6]selenophene is converted into 2-acyl derivatives by reaction with acid chlorides in the presence of aluminum chloride, whereas similar Friedel-Crafts acylation of benzo[6]thiophene yields 3-substituted products. When the 2-position is blocked, formylation can be directed into the 3-position. Thus treatment of 2-bromobenzo[6]selenophene with dichloromethyl butyl ether (Cl2CHOBu) and titanium tetrachloride yields the 3-formyl derivative (72BSF3955). If the 2- and 3-positions of benzo[6]selenophene are blocked with methyl groups, acylation under Friedel-Crafts conditions occurs in the 6-position (78CR(C)(287)333>. 

The syntheses of 2-ketobenzo[ >]selenophene (134) (76JCS(P1)2452) and its benzo[c] counterpart (135) (64BSB491, 81JHC343) both depend on intramolecular acylation of an intermediary selenol, while in the benzo[Z>]selenophene (137) preparation from (136) the ring closure depends upon the intramolecular addition of the intermediary selenol to the carbonyl group (70BSB235). 

The bromination, acetylation, and mercuration of benzo[6]selenophen have been studied by Russian workers. 2-Methylbenzo[6]selenophen is acylated and brominated in the 3-position, whereas the 3-methyl isomer reacts in the 3-position. The nitrosation of (672) is claimed to yield (673), which was reduced and acetylated to (674). From this compound, the... 

Russian workers have worked out another approach to benzo-[bjselenophens starting from selenophen derivatives. Acylation of (514) gave (515), which upon treatment with perchloric acid gave the pyrylium salts (516). Upon treatment with secondary amines, (516) gave amino-substituted benzo[b]selenophens, e.g. (517). From the pyrylium salt (518), only (519) was obtained. On treatment of (518) with aqueous hydroxide, (520) was obtained. Other benzo[b]selenophens hydroxylated in the benzene ring have been prepared similarly. Through the condensation of... 

Contrary to benzo[b]thiophen, benzo[b]selenophen is acylated at position 2. 2-Bromobenzo[b]selenophen, prepared from the 2-lithium derivative and bromine, is acylated at position 3, and from this derivative the 3-isomers could be synthesized. A large number of 2- and 3-aroylbenzo[b]seleno-phens were synthesized, either by Friedel-Crafts reaction of benzo-[bjselenophencarboxylic acid chlorides and benzenes or from benzol bjselenophens and benzoic acid chlorides. Also the reaction between Grignard reagents and nitriles was used for the synthesis of aroylbenzo[b]selenophens. 4,S-Diaminobenzo[b]selenophen has been synthesized via nitration of 5-aminobenzo[b]selenophen or via the reaction of the diazonium salt derived from the S-amino-derivative with p-sulphanilic acid. From the diamino-derivative, several fused benzo[b]selenophens, e.g. (525), (526), and (527), were prepared. Reaction of the phenyl-... 

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