Benzoselenophenes, synthesis

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... 

The 1-benzoselenophenes are relatively stable and easy to manipulate. Their synthesis has been extensively studied since some of them are analogs of naturally occurring biologically active 1-benzofurans, 1-benzothiophenes, and indoles [1,14, 118, 120],... 

An expedient method for synthesis of 2,3-disubstituted 1-benzoselenophenes (91) by the electrophilic cyclization of various 1 -(1 -alkynyl)-2-(methylseleno)arenes (90) has been reported recently (Scheme 24). This method tolerates a wide of variety of functional groups, and proceeds under exceptionally mild reaction conditions [141], Moreover, an efficient solid phase synthesis of 91 based on a combination of palladium-mediated coupling and iodocyclization protocols has been developed [142],... 

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. 

In common with related heterocycles, 2-benzoselenophene is unstable and cannot be isolated but can be stored in solution and easily undergoes the Diels-Alder reaction [146], In contrast, the 1,3-disubstituted 2-benzoselenophenes are stable compounds and synthesis of 1,3-dicyano 2-benzoselenophene (97) starting from o-xylene dicyanide (96) using SeOCL, as selenium transfer reagent was reported (Scheme 27) [147],... 

There are no reports on ring synthesis of nonfused isoselenazoles by transformation of another ring although two reactions afford 3-substituted benzisoselenazoles. On treatment first with bromine and then with ammonia, 1-benzoselenophene-2,3-dione undergoes ring transformation to afford 3-carbamoylbenzisoselenazole (Scheme 51) <1975JHC1091>. 

The benzoselenophene phosphonic acid (128) has been obtained from phenyl-ethynylphosphonic acid and Se02-HBr" and classical reactions were employed in the synthesis of the pyridone acids (129) (R = aryl or heteroaryl, R = H or COOMe). ... 

Benzoselenophene [111, 112] and related fused selenophenes [113-116] were previously obtained via tedious multistep reactions involving a selenocyclization reaction from barely accessible selenium-containing compounds. Such conventional synthetic methods are unsuitable for the development of selenophene-based OFET materials. Sashida s group developed a simple one-pot preparation of benzoselenophenes by an intramolecular selenocyclization reaction of acetylene compounds with a selenolate anion [117, 118]. This allowed straightforward access to sophisticated fused selenophenes, such as 52 and 53, from commercially available chemicals [119, 120]. Scheme 6.9 depicts the key selenocyclization reaction used in the synthesis of 52. This synthetic protocol was also successfully applied to the synthesis of regioisomer 54 [121]. 

Diselenium dichloride added dropwise to a stirred soln. of the startg. m. in abs. dimethylformamide 2-n-butyl-3-chloro-l-benzoselenophene. Y 41%. F. e. and products s. W. Ried and G. Sell, Synthesis 1976, 447. 

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