The first method to access unsymmetrical aliphatic acyloins is presented. The method relies on a fast 1,3‐hydride shift mediated by an IrIII complex in allylic alcohols followed by oxidation with TEMPO+. The direct conversion of allylic alcohols into acyloins is achieved in a one‐pot procedure. Further functionalization of the Cα′ of the α‐amino‐oxylated ketone products gives access to highly functionalized
Stereoconvergent Synthesis of Chiral Allylboronates from an <i>E</i>/<i>Z</i> Mixture of Allylic Aryl Ethers Using a 6-NHC−Cu(I) Catalyst
作者:Jin Kyoon Park、Hershel H. Lackey、Brian A. Ondrusek、D. Tyler McQuade
DOI:10.1021/ja1112518
日期:2011.3.2
We present a 6-NHC-Cu(I) complex that provides alpha-substituted allylboronates using allylic aryl ether substrates. The method was discovered by comparison of the chemoselectivities exhibited by complexes 1a, 1b, 2, and 3. We observed that 1a preferentially reacts with electron-rich alkenes over electron-deficient alkenes. Development of an asymmetric method revealed that 1b reacts with both the E and Z isomers to provide the same absolute configuration without showing E-Z isomerization. This stereoconvergent reaction occurs with high yields (av 86%), high S(N)2` selectivity (> 99:1), and high ee (av 94%) and exhibits wide functional-group tolerance using pure E or Z isomer or E/Z alkene mixtures. The stereoconvergent feature enables the use of many different olefination strategies for substrate production, including cross-metathesis. Chiral allylboronates could be purified by silica gel chromatography and stored in the freezer without decomposition.
Enantioselective Synthesis of Cyclic Nitrones by Chemoselective Intramolecular Allylic Alkylation of Oximes
作者:Tobias Sandmeier、Erick M. Carreira
DOI:10.1002/anie.202100150
日期:2021.4.26
The enantio‐ and chemoselective iridium‐catalyzed N‐allylation of oximes is described for the first time. Intramolecular kinetic resolution provides access to cyclicnitrones and enantioenriched aliphatic allylic alcohols. Salient features of this transformation are its ability to employ E/Z‐isomeric mixtures of oxime starting materials convergently and high functional group tolerance. The implementation