2- Substituted tellurophenes

The effects of 2- and 3-substituents on the 77Se NMR chemical shifts in selenophene and benzolb]selenophene have been investigated in detail (75CS(8)8, 8lOMR(l6)14). The 125Te shifts in 2-substituted tellurophenes exactly parallel the 77Se shifts in similarly substituted selenophenes (76CS(10)139>. 

The JH NMR spectra of 2-substituted tellurophenes have also been systematically studied (76ACS(B)605). As in the selenophene series, a-protons resonate at lower field than /3-protons. Coupling constants are also in the order J45 >J34>J3s- The magnitude of the coupling constants observed for tellurophene derivatives is greater than those of the corresponding selenophenes and thiophenes. 

Methyltellurophene and 2-iodotellurophene - but not a series of other 2-substituted tellurophenes - are reported to react with tetramethylsilane in acetone6. 2,3-Dihydrotellurophenes, 2,5-dihydrotellurophenes, and tetrahydrotellurophenes are discussed in the section on diorgano telluriums (p. 378, 408, 430, 431). 

When l-formyl-2-chlorocydoalk-l-enes were used as starting materials, polycyclic ring systems containing the 2-substituted tellurophene ring were obtained in yields not exceeding 30%... 

Data on H NMR spectral parameters of tellurophene <1972J(P1)199, 1974MP257>, 2-substituted tellurophenes <1974ACB175, 1976ACB605> and, for comparison, furan, thiophene and selenophene <1965SA85> are listed in Table 3. 

Table 3 NMR parameters for tellurophene and congenerous rings (in CDCI3) and 2-substituted tellurophenes 2-RC4H3X...

Te chemical shifts in 2-substituted tellurophenes <1976CS139, 1981ZOR947, 1982MR504> are given in... 

The tellurophene is formed via a first Te-C sp cleavage followed by an unusual Te-C sp cleavage. The treatment of the reaction mixture with benzaldehyde or with elemental selenium followed by ethyl bromide affords the 2-substituted tellurophenes. 

The dipole moments in benzene of a number of 2-substituted tellurophenes have been determined13 and compared with the moments of the corresponding derivatives of furan, thiophene, and selenophene (Table V). 

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