Synthesis of tetrathia[7]helicene based phosphorus derivatives

Tetrathia[7]helicenes (7-TH) are polyconjugated π-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, making it possible the introduction of appropriate substituents.2 In the course of our studies on the synthesis of phosphorus derivatives of 7-TH as chiral ligands in asymmetric catalysis,3 several 7-TH mono or diphosphanes 1 and mono or diphosphine oxides 2 have been selectively prepared and characterized (Figure 1). Figure 1 Phosphanes 1 and phosphine oxides 2 represent novel and promising chiral Lewis bases to use in asymmetric organocatalysis.