(3 + 3) Cycloaddition of Oxyallyl Cations with Nitrones: Diastereoselective Access to 1,2-Oxazinanes
作者:Marie Cordier、Alexis Archambeau
DOI:10.1021/acs.orglett.8b00617
日期:2018.4.20
Oxyallylcations are prepared in situ from readily available α-tosyloxy ketones and act as transient electrophilic partners in (3 + 3) cycloaddition with nitrones. Under mild conditions, this method provides a chemoselective and diastereoselective route to polysubstituted 1,2-oxazinanes. A stepwise process is proposed to rationalize the diastereoselectivity of this transformation.
SmI<sub>2</sub>-Promoted Radical Addition of Nitrones to α,β-Unsaturated Amides and Esters: Synthesis of γ-Amino Acids via a Nitrogen Equivalent to the Ketyl Radical
作者:Ditte Riber、Troels Skrydstrup
DOI:10.1021/ol027386y
日期:2003.1.1
[reaction: see text] Alkyl nitrones undergo radical addition reactions to a series of alpha,beta-unsaturated amides and esters when subjected to samarium diiodide via a nitrogen equivalent to a ketyl radical anion. This reaction conveniently provides access to a variety of functionalized gamma-amino acids. The methodology was extended to the asymmetric synthesis of 4-substituted gamma-amino acids,
The scope and potential of the reaction have been investigated and developed. The reaction can also be catalyzed by secondaryamines. The use of chiral cyclic amines, such as L-proline leads to optically active beta-hydroxynitrones in moderate yield and with moderate to high enantiomeric excess. The reaction mechanism was studied by kinetic measurements, intermediate and product analysis, and determination
Methods for the preparation of substituted homoallylic amines and their conversion to pyrrolidines or pyrrolizidines are described. N-Alkylation of a variety of homoallylic secondary amines with (tributylstannyl)methyl methanesulfonate and subsequent tin-lithium exchange, generates organolithium species that undergo intramolecular carbolithiation (anionic cyclization). High stereoselectivities in the cyclization, particularly for the formation of 2,4-disubstituted pyrrolidines, are obtained.