Selenophenes lithiation

Thieno[2,3 -h]selenophenes lithiation, 4, 950 Thienospirans synthesis, 4, 760 Thieno[3,4-c][l,2,5]thiadiazoles cycloaddition reactions, 6, 534 reactions, 6, 1036 synthesis, 6, 1042, 1044 Thieno[2,3-d]thiazole, 2-acylamino-synthesis, 6, 1010 Thieno[2,3-d]thiazoles synthesis, 5, 116 6, 988, 994 Thieno[3,2-d]thiazoles synthesis, 5, 135 6, 1015 Thieno[3,4-d]thiazolidine-2-thione, perhydro-... 

Selenophene, bis(TV-chlorothioimino)-molecular structure, 4, 939 Selenophene, 2-bromo-mercuration, 4, 946 Selenophene, 3-bromo-lithiation, 4, 949 synthesis, 4, 955 Selenophene, 3-bromo-2-lithio-synthesis, 4, 955 Selenophene, bromonitro-debromination, 4, 78 synthesis, 4, 955 Selenophene, 2-chloromethyl-solvolysis, 4, 952 Selenophene, 3-cyano-synthesis, 4, 955 Selenophene, deutero-deuterium exchange, 4, 949 Selenophene, 2,5-diacyl-3,4-dihydroxy-synthesis, 4, 964... 

Selenophene, 2,5-diamino-3,4-dicyano-synthesis, 4, 119, 964 Selenophene, 2,4-diaryl-synthesis, 4, 967 UV spectra, 4, 941 Selenophene, 2,5-diaryl-synthesis, 4, 967, 969 UV spectra, 4, 941 Selenophene, 2,5-dichloro-metallation, 4, 949 Selenophene, dihydro-3-methylene-synthesis, 4, 963 Selenophene, 2,5-dimethoxy-lithiation, 4, 949 Selenophene, 2,4-dimethyl-... 

Selenophene, 2,5-dimethyl-3-mercapto-synthesis, 4, 956 tautomerism, 4, 946 Selenophene, 2,4-diphenyl-synthesis, 4, 135 Selenophene, 2,5-diphenyl-lithiation, 4, 949 UV spectra, 4, 941 Selenophene, 2-ethoxycarbonyl-mercuration, 4, 946 Selenophene, halo-reactions, 4, 955 Selenophene, 2-hydroxy-Michael reaction, 4, 953 tautomerism, 4, 36, 945, 953 Selenophene, 3-hydroxy-tautomerism, 4, 36, 945 Selenophene, 3-hydroxy-2,5-dimethyl-tautomerism, 4, 945, 953 Selenophene, 2-hydroxy-5-methyl-methylation, 4, 953 tautomerism, 4, 945 Selenophene, 2-hydroxy-5-methylthio-tautomerism, 4, 945 Selenophene, 3-iodo-synthesis, 4, 955 Selenophene, 3-lithio-reactions, 4, 79 synthesis, 4, 955 Selenophene, 2-mercapto-tautomerism, 4, 38 Selenophene, 3-mercapto-tautomerism, 4, 38 Selenophene, 2-mercapto-5-methyl-synthesis, 4, 956 tautomerism, 4, 946 Selenophene, 3-methoxy-lithiation, 4, 949, 955 synthesis, 4, 955 Selenophene, methyl-oxidation, 4, 951 synthesis, 4, 963 Selenophene, 2-methyl-lithiation, 4, 949 Selenophene, 3-methyl-synthesis, 4, 963... 

Lithiated selenophenes and tellurophenes have been used as intermediates in the preparation of a wide range of derivatives. A comprehensive tabulation of these transformations is available (790R(26)l) and this illustrates the large number of electrophiles which have been reacted with selenienyl- and, to a lesser extent, tellurienyl-lithiums. An extension of the synthetic potential of these lithiated derivatives is achieved by first converting them into iodonium salts (111), which may then be reacted with nucleophiles (Scheme 12) (74SC63). 

The l-methylbenzo[A]thieno[2,3-/)]pyrrole (149) and benzo[6]selenolo[2,3-6]pyrrole (150) were prepared (83JHC49) and the influence of annelation and of the heteroatom upon the reactivity towards acetylation and lithiation was investigated <83JHC6l>. The sulfur and selenium analogues with [h,2-b (75)-(77) and [2,3-b (149) and (150) annelation were acetylated at C-2 and C-3. No reaction at all was observed with butyllithium except in the case of 1 -methylbenzo[6]selenolo[2,3-/ ]pyrrole (150), where the opening of the selenophene nucleus, after car-boxylation and the action of diazomethane, gave l-methyl-2-methoxycarbonyl-3-(2 -methyl-selenophenyl)pyrrole (151) and the positional isomer (152). 

Selenophene is 1.5 times more reactive than thiophene toward lithiation by PhjCLi. Selenophene (71CHE938) and tellurophene [76ACS(B)605] are preferentially lithiated in the 2-position. Selenophene sulfonates at the 2-position, and 2-methyl-, 2-carboxy-, and 2-formylselenophene sulfonate at the 5-position (64JGU 1814,2201). Towards protiodemercuriation at the 2-position, selenophene is either slightly more or less reactive than furan, depending on the reaction temperature (65AJC1513). 

A few three-component reaction sequences leading to selenophenes have been reported. Lithiation of diphenylace-tylene followed by treatment with elemental selenium led to 2,3,4,5-tetraphenylselenophene 121 (Equation 20) <1999JOM(573)267>. 

Determination of the relative kinetic acidities of the 2- and 3-protons in thiophene (H/D exchange experiments) shows the 2-proton to be 500 times more acidic than the 3-proton [127]. However, when a sufficient amount of HMPT is added to a solution of 2-lithiothiophene, ring opening to LiC=C—CH=CH—SLi occurs, which means that under these conditions exchange between Li and the 3-proton can take place [128]. Selenophene [129] and tellurophene [130] have been lithiated with satisfactory results. We have the impression however, that a more careful control of the reaction conditions is required, and bases with a more moderate reactivity, such as EtLi LiBr in Et20, seem to give better results, especially in the case of tellurophene [9]. 

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