Abstract
A mild and efficient protocol for P-C bond formation was developed with sub-stoichiometric amounts of copper iodide as a catalyst. A series of sterically and electronically divergent phosphineboranes were subjected to coupling reactions and the corresponding products were obtained in high yields with retention of configuration. The reaction proceeded under non-basic conditions thus avoiding base-catalyzed racemization.
Key words
tertiary phosphineboranes - phosphorylation - ethyl diazoacetate - pseudorotation
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11
[(
R
)
-
(Ethoxycarbonylmethyl)phenylmethylphosphino]-borane (
2a); Typical Procedure A mixture of 1 (138 mg, 1.0 mmol), CuI (9.5 mg, 0.05 mmol, 5 mol%), and diazo compound (136 mg, 1.2 mmol) was dissolved in MeCN and the resulting solution was stirred at ambient temperature. After 3 h, the reaction mixture was quenched with a sat. solution of NH4 Cl, and the aqueous layer was extracted with EtOAc. The combined extracts were washed with a sat. solution of NaCl and dried over anhyd Na2 SO4 . The solvent was evaporated under reduced pressure and the resulting residue was subjected to column chromatography on silica gel (EtOAc-hexane, 2:8) to give (Rp
)-2a (212 mg) in 95% yield as a colorless oil; [α]D
25 -5.9 (c 1.0, benzene). 1 H NMR (200 MHz, CDCl3 ): δ = 1.15 (t, J = 6.77 Hz, 3 H), 1.80 (d, 3
J
P-H = 10.16 Hz, 3 H), 2.80-2.95 (m, 2 H), 4.00 (q, J = 4.23, 7.6 Hz, 2 H), 7.40-7.55 (m, 3 H), 7.65-7.80 (m, 2 H). MS (70 eV): m /z (%) = 224 (M+ , 24).
