New chiral monodentate phospholane ligands by highly stereoselective hydrophosphination

New chiral phospholanes 6 were prepared in both enantiomeric forms starting from l- and d-tartaric acid. The key step in the synthetic sequence is the double hydrophosphination of unsaturated chiral bis(lactone) 9 by NaPhPH(BH3). This method was used for the first time in the formation of chiral phospholanes. The structure of phospholane 6a was confirmed by X-ray crystallography. σ-Donor properties of the phospholanes were estimated by measurement of 1J(31P–77Se) coupling constants in the corresponding phosphine selenides. The new phospholanes were tested as ligands in the Rh-catalyzed enantioselective hydrogenation of functionalized standard olefins (65–92% ee).

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(3aR,4aR,7aR,7bR)-4-Phenylperhydrofuro[2′,3′:4,5]phospholo[3,2-b]furan-2,6-dione–BH3 complexC14H16BO4PDe = >99%, ee = >99%[α]D25=+74.25 (c 2.97, CHCl3)Source of chirality: natural l-(+)-tartaric acid

(3aS,4aS,7aS,7bS)-4-Cyclohexylperhydrofuro[2′,3′:4,5]phospholo[3,2-b]furan-2,6-dione–BH3 complexC14H22BO4PDe = >99%, ee = >99%[α]D21=+33.5 (c 5, acetone)Source of chirality: natural l-(+)-tartaric acid