Macrocycles based only on thiophenes

Linkages including -positions of thiophene units leading to cross-conjugated cyclo[n]thiophenes 

Cyclobutadithiophene 4.1 can formally be regarded as the smallest member of the cyclothiophenes. Also known as cyclo [2]thiophene or cyclodi(3,4-thienylene), it was prepared by Shepherd as the most stable of the four possible isomeric dithia analogues of biphenylene [356]. In the NMR spectrum of 4.1, a paramagnetic shift of the a-thiophene protons has been found, indicating a cyclobutadienoid or [4]annulenoid structure. In the UV spectrum, absorptions are red shifted (334, 318 nm) compared with that of thiophene (230 nm), providing evidence of electronic interaction and conjugation between the two thiophene units. 

In addition, lyoda et al. reported the synthesis of variants of tetra(2,3-thienylene) which are planar, in contrast to Marsella et al. s derivatives [369]. With respect to thiophene-based [12]annulene 4.9, which was first synthesized by Kauffmann et al. in low yields, Marsella s group extended this scaffold by preparing 

The feasibility and importance of fully a-conjugated cyclothiophenes was supported by theoretical calculations which were carried out in 1995 by Tol on cyclo [12]thiophene and on its corresponding charged 

---