Diastereo- and Enantioselective Synthesis of (E)-2-Methyl-1,2-syn- and (E)-2-Methyl-1,2-anti-3-pentenediols via Allenylboronate Kinetic Resolution with ((d)Ipc)(2)BH and Aldehyde Allylboration

Department of Chemistry, Scripps Florida, Jupiter, Florida 33458, USA.
Organic Letters (Impact Factor: 6.36). 05/2012; 14(12):3028-31. DOI: 10.1021/ol3010968
Source: PubMed


Enantioselective hydroboration of racemic allenylboronate (±)-1 with 0.48 equiv of ((d)Ipc)(2)BH at -25 °C proceeds with efficient kinetic resolution and provides allylborane (R)-Z-4. When heated to 95 °C, allylborane (R)-Z-4 isomerizes to the thermodynamically more stable allylborane isomer (S)-E-7. Subsequent allylboration of aldehydes with (R)-Z-4 or (S)-E-7 at -78 °C followed by oxidative workup provides 1,2-syn- or 1,2-anti-diols, 2 or 3, respectively, in 87-94% ee.

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