Benzo- selenophene

The first proton to be removed from N-methylpyrrole by n-butyllithium is from an a-position a second deprotonation occurs to give a mixture of 2,4- and 2,5-dilithiated derivatives. The formation of a 2,4-dilithio derivative is noteworthy since in the case of both furan and thiophene initial abstraction of a proton at C-2 is followed by proton abstraction from C-5 (77JCS(P1)887). Af-Methylindole, benzo[ >]furan and benzo[ >]thiophene are also deprotonated at C-2. Selenophene and benzo[ >]selenophene and tellurophene and benzo[6]tellurophene similarly yield 2-lithio derivatives (77AHC(2l)ll9). 

Murphy J (2000) Benzo[ ]selenophenes. In Houben-Weil science of synthesis. Thieme, Stuttgart, chap 10.7, p 265... 

The reaction between benzyne derivatives and selenium analogues of Barton s thiopyridone esters provided a convenient entry into complex, fused benzo[3]selenophenes <2004JHC13, 2004ARK51>. For example, the generation of the benzyne 86 in the presence of selenoester 85 provided benzo[. ]seleno[2,3-. ]pyridine 87, presumably via a single electron transfer (SET) pathway (Equation 11). This methodology was examined utilizing a number of benzyne precursors (anthranilic acids, iodium triflates, and trimethysilyl triflates) and provided access to an impressive number of fused benzo[. ]selenophenes. 

The gas-phase thermal reaction of cinnamaldehyde with dimethyl diselenide at 630 °C gave benzo[ ]selenophene 2 <1998RCB447>. 

An alkyltelluride-mediated reductive cyclization provided a route to benzo[/ ]selenophenes that are potential antioxidants <1999JOC6764>. 

Syntheses of benzo[Z>]telluroles, benzo[/)]selenophenes and dibenzotellurolo [3,4-Z>]tellurole 01YGK355. 

Benzylseleno-l-(2-iodophenyl)ethanol reacts smoothly with tris(trimethylsilyl)silane to give benzo[ ]selenophene (eq 13). A similar homolytic substitution reaction at the silicon atom yields a sila bicycle. ... 

This methodology can be extended to the synthesis of disubstituted benzo[ ]selenophenes 54 from the selenide 53, which was readily accessible Irom o-iodoaniline in three steps, by using platinum catalyst (Scheme 27.21) [26]. 

The orf/zo-alkenylarylzinc reagent obtained by the migratory arylzincation serves as a precursor to benzo[ijchalcogenophenes such as benzo[fe]thiophenes and benzo[h]selenophenes (Scheme 10.9) [28]. Treatment of the zinc intermediate with sulfur powder in the presence of Cul allows one-pot synthesis of a benzo[h]thiophene derivative (route A). Alternatively, the zinc intermediate is quenched with iodine to give ortho-alkenylaryl iodide, which is then subjected to copper-catalyzed reaction with sulfur or selenium powder to furnish the corresponding benzo[i]thiophene or benzo[(i]selenophene derivative (route B). Collectively, these approaches allow for expedient synthesis of functionalized benzo[h]thiophenes and benzo[()]selenophenes, many of which are difficult to... 

The much less sophisticated PPP approximation has been shown to well reproduce the electronic spectral features not only of the monocyclic furan, pyrrole, thiophene, selenophene and tellurophene but also many of the benzo fused derivatives as well (79MI30101, 68JPC3975, 68MI30100). 

The major internal comparisons to be made within this chapter are between (13) pyrrole (1), furan (2), thiophene (3), selenophene (4) and tellurophene (5) b) pyrrole (1) and indole (6) (c) indole (6), benzo[6 Jfuran (7) and benzo[6]thiophene (8) d) indole (6), isoindole (9) and indolizine (10) and (e) benzo[6] and benzo[c] fused systems. The names of relevant heterocyclic radicals are given with the structures of the parent heterocycle. 

Thiophene and selenophene can be chloromethylated by treatment with formaldehyde and hydrochloric acid. Depending on the conditions, 2-chloromethyl or 2,5-bis(chloromethyl) derivatives are obtained. The chloromethylation of benzo[6]thiophene gives the 3-chloromethyl derivative and that of benzo[6]furan the 2-chloromethyl compound (71AHC(13)235). 

Halogens attack the ring heteroatom in selenophene and tellurophene. Thus the selenienyl bromide (89) is among the bromination products of benzo[6]selenophene. Tellurophene reacts with halogens to give 1,1-dihalogeno derivatives e.g. 90). 

Benzo[Z)]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z)]furan and 2- and 3-vinylindoles give adducts involving the exocyclic double bond. In contrast, the benzo[c]-fused heterocycles function as highly reactive dienes in [4 + 2] cycloaddition reactions. Thus benzo[c]furan, isoindole (benzo[c]pyrrole) and benzo[c]thiophene all yield Diels-Alder adducts (137) with maleic anhydride. Adducts of this type are used to characterize these unstable molecules and in a similar way benzo[c]selenophene, which polymerizes on attempted isolation, was characterized by formation of an adduct with tetracyanoethylene (76JA867). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

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... 

Benzo[h]selenophene, 3-bromo-2-lithio-synthesis, 4, 956 Benzo[h]selenophene, 3-chloro-synthesis, 4, 116... 

Benzo[h]seienophene, 2,3-dihydro-2-methyl-synthesis, 4, 961 Benzo[h]selenophene, 3-halo-2-substituted synthesis, 4, 966... 

Ben2o[fa]selenophene, 2-hydroxy-tautomerism, 4, 945 Benzo[h]selenophene, 3-hydroxy-tautomerism, 4, 37, 945 Benzo[h]selenophene, 4-hydroxy-synthesis, 4, 969... 

Benzo[h]selenophene, 7-hydroxy-synthesis, 4, 969 Benzo[h]selenophene, 3-lithio-synthesis, 4, 955 Benzo[h]selenophene, 2-methyl-mass spectra, 4, 942 synthesis, 4, 961 Benzo[h]selenophene, 3-methyl-mass spectra, 4, 942 synthesis, 4, 956... 

Benzo[h]selenophene-2-carboxylic acids ethyl ester synthesis, 4, 959 reactions, 4, 952 synthesis, 4, 95... 

---