The Hydroboration of Propargyl Bromide. Simple One-Pot Three-Component Routes to (<i>Z</i>)-1-Bromoalk-1-en-4-ols and to <i>a</i><i>nti</i>-Homoallylic Alcohols
toward either the synthesis of (Z)-1-bromoalk-1-en-4-ols 6 or anti-homoallylic alcohols 8. Two one-pot three-component processes were developed based on a sequence of four reactions; preparation of dialkylborane and hydroboration of propargyl bromide are the first steps. Then, quaternization with TEBABr may be carried out either in the presence of the aldehyde when (Z)-1-bromoalk-1-en-4-ols 6 are requested
(3-Bromoalken-1-yl)dialkylboranes, generated by hydroboration of propargyl bromide with dialkylboranes, smoothly rearranges to (E)-allylic boranes which can be trapped with aldehydes. The resulting one-pot three-component sequence represents a route to anti-homoallylic alcohols in fairly good yields. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
Diastereo- and Enantioselective Synthesis of <i>syn</i>-α-Vinylchlorohydrins and <i>cis</i>-Vinylepoxides
作者:Shaojing Hu、Seetharaman Jayaraman、Allan C. Oehlschlager
DOI:10.1021/jo960875p
日期:1996.1.1
A new method to generate chiral syn-vinylchlorohydrins and cis-vinyloxiranes is reported. Reaction of (alpha-haloallyl)lithiums with methoxy-9-BBN or Ipc(2)BOMe followed by treatment with BF3 . OEt(2) leads to (Z)-(gamma-haloallyl)boranes which react with aldehydes to yield cis-vinylepoxides (de greater than or equal to 90%) upon oxidative workup. Alternatively, addition of ethanolamine to the allylboration product yields syn-alpha a-halohydrins (de greater than or equal to 90%) that are also easily cyclized to cis-vinylepoxides. Extension of this protocol using [(Z)-gamma-chloroallyl]BIpc(2) leads to chiral syn-alpha-chlorohydrins and cis-vinylepoxides in high de (greater than or equal to 90%) and ee(90-99%). Enantioselectivity of reactions of chiral (Z)-(gamma-chloroallyl)boranes with aldehydes are more sensitive to reaction conditions than enantioselectivity of reactions of other alpha-or gamma-substituted allylboranes. The effects of proportion ofBF(3) . OEt(2) and the relative efficacies of LiNR(2) bases on diastereo- and enantioselectivity of the chloroallylation are reported.
Julia, Marc; Verpeaux, Jean-Noel; Zahneisen, Thomas, Bulletin de la Societe Chimique de France, 1994, vol. 131, p. 539 - 554
作者:Julia, Marc、Verpeaux, Jean-Noel、Zahneisen, Thomas