Chiral Synthesis via Organoboranes. 27. Remarkably Rapid and Exceptionally Enantioselective (Approaching 100percent ee) Allylboration of Representative Aldehydes at -100 deg C under New Salt-Free Conditions

Article abstract of DOI:10.1021/jo00001a072

In the absence of magnesium salts (from the synthesis of the reagents), our chiral B-allylditerpenylborane reagents (Ter2*BCH2CH=CH2), 1-3) react with representative aldehydes (RCHO, R=Me, n-Pr, i-Pr, t-Bu, vinyl, and Ph) practically instantaneously at -100 deg C to give homoallylic alcohols (R*CH(OH)CH=CH2) with optical purities approaching 100percent ee.The exceptional reaction rate achieved at -100 deg C indicates that these allylborations are among the fastest reactions presently known to the organic chemist.The short reaction time adopted (dIpc2BAll, ^d1) give homoallylic alcohols of >/= 98percent ee and B-allylbis(2-isocaranyl)borane (2-^dIcr2BAll, 3) provides alcohols of >/= 99percent ee.The enantioselectivities (>/= 99percent ee) achieved in allylboration by the reagent 3 are essentially perfect, making this one of the most stereoselective reactions currently known in organic chemistry.