Enantioselective Syntheses of syn- and anti-β-Hydroxyallylsilanes Via Allene Hydroboration-Aldehyde Allylboration Reactions
摘要:
The kinetic hydroboration of allenylsilane 5 with ((d)Ipc)(2)BH at -40 degrees C provides allylborane 9Z with >= 12:1 selectivity. When the hydroboration is performed at temperatures above -40 degrees C, 9Z isomerizes to the thermodynamically more stable allylborane 9E with >20:1 selectivity. Subsequent treatment of 9Z or 9E with aldehydes at -78 degrees C provides syn- or anti-beta-hydroxyallylsilanes, 7 or 8, respectively.
The diastereoselectivesynthesis of anti-homoallylic alcohols bearing conjugated (Z)-enynes through a palladium-catalyzed three-component reaction is described. This reaction features a broad substrate scope, good functional group compatibility, and high levels of (Z)-alkene stereocontrol. In this reaction, Pd(0) functions as a catalyst in two fundamental steps of the tandem sequence: 1) the generation
描述了通过钯催化的三组分反应非对映选择性合成带有共轭 ( Z )-烯炔的抗高烯丙醇。该反应具有底物范围广、官能团相容性好、( Z )-烯烃立体控制水平高的特点。在该反应中,Pd(0) 在串联序列的两个基本步骤中充当催化剂:1) 从双功能连接试剂生成硼化 π-烯丙基钯物种,诱导醛的 umpolung 烯丙基化,以及 2) C( sp 2 )−C( sp ) 交叉耦合。所得产物的进一步转化突出了它们的合成效用。
A new synthesis of 2-alkylbuta-1,3-dienes from internal alkenes and 1,4-dichlorobut-2-yne via dialkyl(1,4-dichlorobut-2-en-2-yl)boranes
作者:Akira Arase、Masayuki Hoshi
DOI:10.1039/c39870000531
日期:——
The successive treatment of borane in tetrahydrofuran with sterically-hindered internalalkenes, 1,4-dichlorobut-2-yne, and alkyl-lithium has provided good yields of 2-alkylbuta-1,3-dienes whose alkyl groups are derived from the alkene.
Diastereoselective synthesis of (Z)- and (E)-homoallylic alcohols using a Pd-catalyzed three-component reaction of 3-(pinacolatoboryl)allyl benzoates, aldehydes, and aryl stannanes was developed, which provides an alternative method for the allylboration of aldehydes using α,γ-diaryl-substituted allylboronates. Both sets of reaction conditions enable access to either (Z)- or (E)-homoallylic alcohols
Regioselectivity of 1,3-Dipolar Cycloadditions of Benzonitrile Oxide to Alkenyl Boronic Esters: An Experimental and Computational Study
作者:Jo Jeong、Kyukwan Zong、Joong Chul Choe
DOI:10.1002/jhet.2667
日期:2017.3
1,3‐Dipolar cycloaddition reactions of benzonitrileoxide to monosubstituted or 1,1‐disubstituted alkenyl boronic ester gave only 2‐isoxazolines, bearing the boronic ester group at the 5‐position of the ring. On the other hand, the cycloaddition reactions of benzonitrileoxide with trans‐1,2‐disubstituted alkenyl boronic esters produced 2‐isoxazolines, bearing the boronic ester group at the 4‐position