The synthesis of new functionalized 1,2-bis(benzodithienyl)ethenes as well as the preparation of the new tetrathia[7]helicenes are described. The helicenes reported are new chiral pushpull molecules, with potential application in optoelectronics.[n]Heterohelicenes are very interesting all conjugated aromatic systems in which heteroaromatic units alternates with arene rings in an extended p-system. 1 When the number of ortho condensed rings [n] exceeds three, these systems are no more planar and they become chiral. The interconversion barrier between the two enantiomers depends on the number of aromatic rings and, for [n] greater than four, they are stereochemically stable compounds which means that their enantiomers can be separated and stored. 2The presence of heterocyclic rings can give some advantages with respect to carbohelicenes. In principle, it is possible to functionalize the heteroaromatic system regioselectively, thus opening the way for obtaining modified helicenes targeted for specific uses, and the tuning and monitoring of their properties. In particular, quite recently, tetrathia[7]helicenes ([7]THs) have attracted a great attention as potential new molecules with interesting optoelectronic properties. 3 In fact, both theoretical calculations 3b,c and experimental work 3a indicate them as new promising candidates for applications in non-linear optics. In particular, the computational study suggests that the presence of some appropriate electron-withdrawing and electron-donating substituents in the positions 2, 7, 8 and 13 of the helical system should improve their optoelectronic responses. 3c In addition to the above-mentioned potentialities, suitable functionalized [7]THs could be very interesting also as new chiral ligands to be use in catalysis. 4 For all these reasons, the search of new methods for the preparation of [7]THs and their functionalization is a highly desirable goal. Recently, 5 we have set up a new efficient synthesis of substituted [7]THs based on a Suzuki coupling of diboronic esters derivatives. More recently 6 we have studied new silyl substituted [7]THs, useful for the access to variously functionalized derivatives.In this paper we describe the preparation of [7]THs decorated with both electron-donating and electron-withdrawing substituents, in view of studying their non-linear optical properties. In particular, we focused our attention on the introduction of electron-donating and electronScheme 1 Strategies for the synthesis of substituted tetrathia[7]helicenes.
Benzothiophene derivatives R 0100 Novel Substituted Tetrathia[7]helicenes by Direct Functionalization of the Helical System or Photocyclization of Substituted 1,2-(Bis-benzodithienyl)ethenes. -(RIGAMONTI, C.; TICOZZELLI, M. T.; BOSSI, A.; LICANDRO*, E.; GIANNINI, C.; MAIORANA, S.; Heterocycles
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