Improved dimethylzinc-promoted vinylation of nitrones with vinylboronic esters
摘要:
Vinylboronic esters derived from 4,4,6-trimethyl-[1,3,2]dioxaborinane react with nitrones in the presence of dimethylzinc; nucleophilic addition of the vinyl group onto nitrones produces N-allylic hydroxylamines in fair yields. The sequence is compatible with various functional groups on the vinylic moiety. The mechanism and kinetic aspects are discussed on the basis of DFT calculations. (C) 2010 Elsevier B. V. All rights reserved.
Methylpentanediolborane: Easy Access to New Air- and Chromatography-Stable, Highly Functionalized Vinylboronates
摘要:
Methylpentanediolborane (MPBH) 1 can be prepared easily by reaction of hexyleneglycol with BH3/DMS or B2H6 generated from NaBH4 and I-2. MPBH hydroborates stereo- and regioselectively highly functionalized alkynes, including propargyl bromide and propionaldehyde acetal. MPBH compares favorably with pinacolborane in terms of reactivity. The obtained vinylboronic esters are air- and chromatography-stable.
Ligand-controlled reactivity plays an important role in transition-metal catalysis, enabling a vast number of efficient transformations to be discovered and developed. However, a single ligand is generally used to promote all steps of the catalytic cycle (e.g., oxidative addition, reductive elimination), a requirement that makes ligand design challenging and limits its generality, especially in relay