Penta-and hexa(3,4-thienylene)s (5T and 6T) were synthesized via sequential Suzuki-Miyaura cross-coupling and Ni(0)-mediated intramolecular homocoupling reactions (Figs. and). For that purpose, diborylthiophene 1 and 4,4ʹdibromo-3,3ʹ-bithiophene (3) were prepared initially according to reported methods. The Suzuki-Miyaura cross-coupling reaction of 1 with an excess of 3 (8.0 equiv.) was carried out using Pd2(dba)3 (2.5 mol%), XPhos (10 mol%), and K3PO4 (4.0 equiv.) to produce dibromoquinquethiophene 4 in 77% yield. Dibromobithiophene 3 was used in excess in order to suppress the generation of polymers. The resulting 4 was treated with Ni(cod)2 (2.2 equiv.) and 2,2ʹ-bipyridine (2.2 equiv.) for 3 h in refluxing tetrahydrofuran (THF) (2 mM), which allowed isolating the desired cyclic oligothiophene (5T) in 36% yield. Increasing the substrate concentration provided 5T in low yield in this reaction step. Next, a cyclic oligothiophene containing an additional thiophene ring, 6T, was synthesized by applying analogous reaction conditions. A borylation reaction similar to that used to synthesize 1 was performed to obtain 4 in 48% yield. The reaction of 4 with an excess of 3 under Pd catalysis furnished dibromosexithiophene 5 in 52% yield. The obtained 5 was subsequently treated with Ni(cod)2 (3.3 equiv.) and 2,2bipyridine (3.3 equiv.) in THF. In contrast to 5T, 6T was obtained in low yield (1.5%, 3.1 mg). To identify the thus-obtained compounds 5T and and to investigate their size-dependent structural characteristics, NMR spectra were recorded (Fig. ). In the room-temperature 1 H NMR spectrum of 5T in dichloromethane-d2, the α-protons of the thiophene rings appear as a singlet at 7.01 ppm. Even at -95 °C, the singlet remains almost unchanged. In the C NMR spectrum in chloroform-d1, two signals were observed at 124.6 and 137.6 ppm. These results indicate that the dynamic interconversion of the thiophene rings is fast on the NMR timescale. Unlike that of 5T, the 1 H NMR spectrum of 6T in dichloromethane-d2 at room temperature displays three signals, i.e., doublets at 6.5 and 6.9 ppm as well as a singlet at 7.3 ppm. Only very slight broadening of the signals was observed even at 140 °C in tetrachloroethane-d2. The 1 H NMR spectra of 4T-6T presented in Fig. clearly demonstrate the size dependence of the symmetry in solution.