Conversion of Conjugated Enones into Enantiomerically Pure ‐Hydroxy Ketones or 1,3‐Diols – Samarium(II) Bromide Reductions of Protected ,‐Dihydroxy Ketones
Asymmetric dihydroxylations of α,β-unsaturated ketones in the presence of Sharpless' AD mix-β™ delivered α,β-dihydroxy ketones or, if phenylboronic acid was present, the corresponding phenylboronates. The C α ―O bonds of these species were removed at ―78 °C ― in the former case after acetonide formation, in the latter case directly ― in an unprecedented manner, namely by treatment with a suspension of Sm II bromide in THF/MeOH. The resulting monohydroxy ketones could be reduced if so desired to give syn- or anti-configured 1,3-diols. The same diols were produced in one-pot reductions of the α,β-dihydroxy ketone diacetonides with Sm II bromide at 0 °C. When the α,β-dihydroxy ketone phenylboronates were treated likewise, the phenylboronates of the 1,3-diols were obtained. Diastereocontrol in the one-pot reductions varied from perfect to nearly absent.