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 (dIpc)2BH and Aldehyde Allylboration
2012
Han, Jeng-Liang | Chen, Ming | Roush, William R.
Enantioselective hydroboration of racemic allenylboronate (±)-1 with 0.48 equiv of (ᵈIpc)₂BH 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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