Elongation and Contraction of Molecular Springs. Synthesis, Structures, and Properties of Bridged [7]Thiaheterohelicenes

Abstract

A series of bridged [7]thiaheterohelicenes 3a-c and 4 with a variety of helical pitches have been prepared from racemic and optical pure 2,13-bis(hydroxymethyl)dithieno[3,2-e:3',2'-e']benzo[1,2-b:4,3-b']bis[1]benzothiophene (1) in order to investigate the helical structures in solution. Recrystallizations of (PM)-3a, (PM)-3b, (PM)-3c, and (P)-4 from hexane-dichloromethane gave crystals suitable for X-ray crystallography, while recrystallization of (PM)-4 with benzene gave an inclusion complex with a stoichiometry of (PM-4)(4).(C(6)H(6)). X-ray analyses of (PM)-3a-c, (PM-4)(4).(C(6)H(6)), and (P)-4 indicate that the dihedral angles between terminal thiophene rings of the helical framework significantly vary from 22 degrees for 4 to 59 degrees for 3c. This represents as increase of 37 degrees or 168%. Although the (13)C NMR and UV absorption spectra of bridged helicenes 3a-c and unbridged helicene 5 are essentially the same, the molar rotation of 5 is very large compared with those of 3a-c and 4. A red shift (15 nm) in the circular dichroism (CD) spectrum is observed for 4, suggesting that this compound is more planar than 3a-c in solution. In the series of [7]thiaheterohelicenes studied, the minimum helical pitch is 2.70 A for 4.

Silyl‐Substituted Tetrathia[7]helicenes: Synthesis, X‐ray Characterization and Reactivity

“…This was confirmed by the X-ray diffraction analysis of a single crystal of 4b, which shows a very large dihedral angle of 59.1(1)°. [14] The crystal structure of compound 4b was determined to elucidate its molecular geometry and crystal packing. The obtained structural parameters were compared with those of the tetrathia [7]helicene, 1 (see Table 2).…”

Helicene-Based Chiral Auxiliaries and Chirogenesis

“…Tanaka et al synthesized bis(hydroxymethyl)thia [7]helicene 174 to study its further synthetic chemistry and corresponding applications in the chirality recognition of biological molecules [97][98][99][100]. Hence, the helicene 174 was synthesized in a total of nine steps with an overall 33% yield, where the photochemical cyclization of alkene 175 was a key step to give silyl group protected rac-176.…”

“…In contrast, although the (M)-180 also showed a 20% reduction, it was observed upon binding both B-and Z-DNA, thus indicating the lack of its discrimination ability. Further, enantiopure alcohol 174 was converted to its dichloride 179, which was converted to 180 [98] and cyclic thia ethers 181-183 [99] using suitable synthetic procedures (Scheme 32). These helicene molecules were explored in terms of possible chiral recognition of biologically relevant molecules such as DNA [98,100].…”

“…Further extending the chiral recognition research of biologically important molecules resulted in the development of cyclic helicenes with thiaether linkage, 181-183 (Scheme 32) [99,100]. The (M)-enantiomers of 181-183 turned out to be potential inhibitors against telomerase enzyme activity based on the chiral and steric matching, while binding to the G-quadruplex superhelix structure.…”

Electrochemical Capacitive K+ EMIS Chemical Sensor Based on the Dibromoaza[7]helicene as an Ionophore for Potassium Ions Detection

“…These are intriguing polycyclic aromatic compounds that combine a helical structure with a conjugated system , containing more than six benzene rings (carbohelicenes) or seven heteroaromatic rings (heterohelicenes). They possess a rigid helical framework and are very stable towards acids, bases, and relatively high temperatures .…”