Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis

Abstract

Tetrathia[7]helicene-based phosphanes thiaheliphos (2a), nPr-thiaheliphos (2b) and di-nPr-thiaheliphos (2c) have been prepared from the 2,13-dilithio derivatives of thiahelicenes 1a–c by reaction with an excess of Ph2PCl. Protection of the air-sensitive products as BH3 adducts, from which the phosphanes 2a–c are easily regenerated on heating with ethanol, is described. New rhodium(I) complexes 8 and 9 were obtained by reaction of 2c with [Rh(COD)2]+[BF4]– and [BARF]–, respectively, which were converted by oxidation into the chelating phosphane–phosphane oxide RhI complexes 10 and 11. The monophosphane 5 was similarly prepared, andreaction of the dilithio species with ClP(O)(OEt)2 gave the diphosphonate 17, which was characterized by X-ray crystallography. Comparison of data from DFT calculations (B3LYP/SVP) on 2c, 8 and 10 and X-ray data for 17 reveals a strong tension within the thiaheliphos ligands that is partially relaxed by increasing the Rh–P distances and the bite angle of the chelating ligand. Compound (P)-(+)-1c, obtained by chromatographic resolution, was transformed into optically pure (P)-(+)-2c, which was used in the asymmetric hydrogenation of itaconic acid ester and methyl 2-acetamidoacrylate (product ees up to 40%)

Rational Design and Synthesis of [5]Helicene-Derived Phosphine Ligands and Their Application in Pd-Catalyzed Asymmetric Reactions

“…Thus, helicenes can be utilized them a broad range of applications in chiral materials, in the chiral recognition of biomolecules, and in asymmetric synthesis161718192021222324. More specifically, chiral helicene-based trivalent phosphorus ligands are efficient asymmetric inductors in metal-catalyzed asymmetric reactions and show good to excellent enantioselectivities252627282930313233. We hypothesized that novel helicenylphosphine ligands, which induce intramolecular metal-arene interactions, could be used to construct an efficient chiral catalytic system.…”

Helical Phosphorus Derivatives

“…Licandro, Froni, and coworkers have also employed the oxidative photocyclodehydrogenation approach for the synthesis of new enantiopure tetrathia-[7]-helicene diphosphine derivative 14 (05SL1137, 06S3670,11EJO5649). A notable feature of this method lies in the fact that the key tetrathia-[7]-helicene scaffold can be easily and regioselectively functionalized at the alpha position of the terminal thienyl rings, thus opening the way for fine-tuning of their reactivity and physicochemical properties.…”

“…As depicted in Scheme 5, the tetrathia-[7]-helicene diphosphine 14 has been employed as ligand in homogeneous asymmetric catalysis (11EJO5649). In particular, itaconic acid ester 7 (Scheme 5(a)) and methyl 2-acetamidoacrylate 15 (Scheme 5(b)) were successfully hydrogenated using a cationic rhodium complex derived from diphosphine (P)-14.…”

Syntheses of Fused Thiophenes: [7]Helicene and Double Helicene Bearing Chiral Alkyl Chains

“…For example, 3 showed [ ] rt D =-1019° (c = 0.001 g/mL, chloroform) [7b] and (-)-hexahelicene (phenanthro [3,4-c]phenanthrene) even gave [ ] 24 D =-3640° (c = 0.098 g/mL, chloroform) [9]. Some helicenes have shown their impressive performance as organic catalysts in asymmetric synthesis [10][11][12][13]. Therefore, the chiral helicenes are extremely attractive *Address correspondence to this author at the Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng, 475004, China; Fax: (+86)-378-3881358; E-mail: hwang@henu.edu.cn to organic chemists.…”