Enantiopure Tetrathia[7]helicene-based Gold(I) Complexes

Tetrathia[7]helicenes (7-TH) are polyconjugated \uf070-systems in which four thiophene rings are orthofused to alternating arene rings to generate a non planar, chiral, stable helix which allows the existence of M and P enantiomers. The 7-TH systems are very interesting structures1 even because they can be easily and selectively functionalized in the alpha positions of the terminal thiophene rings,2 making it possible the introduction of appropriate substituents. In the course of our studies on the synthesis of phosphane derivatives of 7-TH as potential innovative chiral ligands in asymmetric organometallic catalysis,3 gold(I) complexes of the phosphines of 7,8-di-n-propyl-tetrathia[7]helicene 1 and 2 (Figure 1) provided promising results in some cycloisomerization reactions. Figure 1. Encouraged by these results, the two P and M enantiomers of gold(I) complex 1 have been synthesized, and tested in asymmetric transformations. The use of gold in homogeneous catalysis has witnessed tremendous activity in recent years.4 Thanks to gold(I) phosphine-based catalysts, various organic transformations have been accessible with both high yields and chemo- and stereoselectivity. In particular, asymmetric gold catalysis represents a very hot topic in catalytic research,5 and several efforts have been made by various research groups in this field. References 1. Collins, S. K.; Vachon, M. P. Org. Biomol. Chem. 2006, 4, 2518-2524. 2. Licandro, E.; Baldoli, C.; Maiorana, S. et al. Synthesis 2006, 3670-3678. 3. Cauteruccio, S.; Licandro, E.; Maiorana, S. et al. Eur. J. Org. Chem. 2011, 5649-5658. 4. Hashmi, A. S. K.. Chem. Rev. 2007, 107, 3180-3211. 5. Sengupta, S.; Shi, X. ChemCatChem 2010, 2, 609-619