Enantioselective radical-mediated reduction of α-methoxymethyl-α-iododihydrocoumarin 1 using tributyltin hydride is realized in up to 62% enantiomeric excess (e.e.)(88% chemical yield) by combination of chiral diamine 2 and magnesium iodide.
An enantioselective reduction of α-alkyl-α-iododihydrocoumarins 1 by radical-mediated reactions using magnesiumiodide and a chiral diamine 2 is described. The reactions of 1 with tributyltin hydride or triphenyltin hydride in the presence of a chiral Lewis acid generated from magnesiumiodide and 2 at −78°C in ether-CH2Cl2 took place to afford reduced products 3. The determination of the absolute