Synthesis of All Thiophene-Based [7]Helicenes and Trithienothiepines with Isomeric Location of Sulfur Atoms Based on Intramolecular Selectivity of Deprotonation

Abstract

Three unsymmetric thiophene-based [7]helicenes, namely, endo-exo-UH-1, endo-top-UH-2, and exo-top-UH-3, with different isomeric locations of sulfur atoms in two terminal thiophene rings were efficiently synthesized using dithieno[2,3-b:3′,2′-d]thiophene (bb-DTT), dithieno[2,3-b:2′,3′-d]thiophene (bt-DTT), and dithieno[2,3-b:3′,4′-d]thiophene (bs-DTT) as building blocks via Suzuki cross-coupling and intramolecular cyclization reactions. Aside from these racemic [7]helicenes, two novel heterocyclic isomers, namely, trithienothiepines TTTP-1 and TTTP-2, were simultaneously obtained during the intramolecular cyclization. Two novel deprotonations of bi-DTTs and cyclization for synthesizing target compounds showed high selectivity and efficiently constructed both UHs and TTTPs. X-ray crystallographic analyses revealed that the UHs have typical helical molecular structures. The isomeric location of sulfur atoms in the two terminal thiophene rings in endo-exo-UH-1, endo-top-UH-2, exo-top-UH-3, and TTTP-1 allowed multiple intermolecular interactions, such as S•••S, S•••C, and S•••H interactions, resulting in different crystal-packing patterns. Moreover, the absorption behaviors of these [7]helicenes, TTTP-1, and TTTP-2 were examined and theoretically calculated. Results indicated that the isomeric location of sulfur atoms plays a key role in tuning intramolecular π-electronic conjugation.

Synthesis and crystal structures of unsymmetrical wave-shaped heptathienoacenes

“…This general strategy for symmetrical heptathienoacenes or unsymmetrical heptathienoacenes followed by the formation of a C–C bond through CuCl 2 promoted oxidative homocoupling of DTT carbanions or Pd-catalyzed Suzuki cross-coupling of two kinds of DTT isomers. 6–8 Unfortunately, all attempts at the borylation of 2 or 4 were unsuccessful. With a different synthetic strategy, we tried to generate a C–C bond between the two α-positions of 2 and 4 by Negishi cross-coupling.…”

“…To date, a series of the isomers of carbon–sulfur oligomers containing up to seven rings have been reported by Rajca 5 and Wang, 6 such as symmetrical heptathienoacenes including helical, linear and bull's horn structures. Recently, unsymmetrical bull's horn-shaped heptathienoacenes 7 and unsymmetrical thiophene [7]helicenes 8 were rationally designed and synthesized by Wang. Although some symmetrical isomeric heptathienoacenes have been synthesized so far, efficient synthesis methods for unsymmetrical heptathienoacenes are still less developed, and the construction of new molecular skeletons should be paid more attention and effort in the coming years.…”

Thiophene/selenophene-based windmill-shaped triple [6]helicenes

“…11 Wang et al reported novel thiophene-based double helicenes with spiro silicon atoms, “saddle”-formed 8π annulenes, and twisted naphthalenes as central spacers. 9,12 Although great synthetic progress has been achieved in the past two decades, seleno[ n ]helicenes have been rarely reported. In our previous research work, the molecular energy levels of benzohetero[7]helicenes can be precisely modulated by heteroatom replacement of S with Se.…”

Thiophene/selenophene-based S-shaped double helicenes: regioselective synthesis and structures

“…The rapid development of carbohelicenes has led to the synthesis of double, triple, quadruple, quintuple, and sextuple molecules, the chirooptical properties of these molecules, such as their circular dichroism (CD) and circularly polarized luminescence (CPL), have also been widely studied [1][2][3][4][5][6][7][8]. The development of thia-helicene, a class of typical heterohelicenes, has led to the preparation of symmetric thiophene-based [5]-, [7]-, [9]-, and [11]helicenes [9][10][11][12][13][14][15][16], unsymmetric thiophene-based [7]helicenes [17], and thiophene-based double helicenes with spiro-silicon atoms [18], "saddle" formed 8π annulene [12], and twisted naphthalene as central spacers [19].…”