Benzo tellurophene deprotonation

The first proton to be removed from A-methylpyrrole by -butyllithium is from an -position a second deprotonation occurs to give a mixture of 2,4- and 2,5-dilithiated derivatives. In both furan and thiophene, initial abstraction of a proton at C(2) is followed by proton abstraction from C(5). A-Methylindole, benzo[ ]furan, benzo[ ]thiophene, selenophene, benzo[ ]selenophene, tellurophene, and benzo[ ]tellurophene similarly yield 2-lithio derivatives. 

The reactions of the lithio derivatives of benzo[ >]-fused systems indole, benzo[6]furan and benzo[h]thiophene are similarly diverse. Since indole and benzo[h]thiophene undergo electrophilic substitution mainly in the 3-position, the ready availability of 2-lithio derivatives by deprotonation with n-butyllithium is particularly significant and makes available a wide range of otherwise inaccessible compounds. The ready availability of 3-iodoselenophene and hence of 3-lithioselenophene (73CHE845) provides a convenient route to 3-substituted selenophenes. 2-Lithiotellurophenes are especially important precursors of tellurophene derivatives because of the restricted range of electrophilic substitution reactions which are possible on tellurophenes (77AHC(2l)ll9). 

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