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)2BH and aldehyde allylboration.
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.
Department of Chemistry, Scripps Florida, Jupiter, Florida 33458, USA.
Jeng-Liang
JL
Han
Ming
M
Chen
William R
WR
Roush
D000447:Aldehydes / Q000737:chemistry*; D001888:Boric Acids / Q000737:chemistry*; D001896:Boron Compounds / Q000138:chemical synthesis*; D006573:Heterocyclic Compounds, 1-Ring / Q000138:chemical synthesis*; D006865:Hydrogenation; D007700:Kinetics; D008745:Methylation; D015394:Molecular Structure; D013237:Stereoisomerism; D013816:Thermodynamics
D000447:Aldehydes; D001888:Boric Acids; D001896:Boron Compounds; D006573:Heterocyclic Compounds, 1-Ring; C032688:boric acid