这项工作描述了对 α-重氮-β-酮砜的分子内环丙烷化的高度对映选择性不对称催化的发展。我们发现,当 α-重氮-β-酮基甲基砜与新制备的配体 2e 一起使用时,α-重氮-β-酮基砜的催化不对称分子内反应通常以高对映选择性进行。产品的绝对构型已通过 X 射线晶体学分析确定,我们提出的模型 A 和 B 很好地解释了对映选择性的结果。这些产品具有天然产物合成的巨大潜力,因为 (1) 环丙烷的许多不同化学性质、酮、砜都有,(2)产物一般是高度结晶的,
Metal-Free Transfer Hydroiodination of C–C Multiple Bonds
作者:Weiqiang Chen、Johannes C. L. Walker、Martin Oestreich
DOI:10.1021/jacs.8b12318
日期:2019.1.16
The design and a gram-scalesynthesis of a bench-stable cyclohexa-1,4-diene-based surrogate of gaseous hydrogen iodide are described. By initiation with a moderately strong Brønsted acid, hydrogen iodide is transferred from the surrogate onto C-C multiple bonds such as alkynes and allenes without the involvement of free hydrogen iodide. The surrogate fragments into toluene and ethylene, easy-to-remove
描述了基于环己-1,4-二烯的气态碘化氢替代品的设计和克级合成。通过用中等强度的布朗斯台德酸引发,碘化氢从替代物转移到 CC 多重键上,例如炔烃和丙二烯,而没有游离碘化氢的参与。代用品碎片化为甲苯和乙烯,易挥发废物。这种氢碘化反应避免了对碘化氢或氢碘酸的不稳定处理。通过这种方式,可以以立体控制的方式访问范围广泛的以前未知或难以制备的乙烯基碘。
Hexamethyldisilazanes mediated one-pot intramolecular Michael addition–olefination reactions leading to exo-olefinated bicyclo[6.4.0]dodecanes
A novel one-pot reaction for the synthesis of exo-olefinated bicyclo[6.4.0]dodecanes 23 has been developed on the basis of an intramolecular Michael reaction of phenylsulfonyl compounds 4 with potassium hexamethyldisilazide (KHMDS) and a sequential reaction with an excess of methoxymethyl chloride (MOMCl). By this reaction, an exo-olefin group was regioselectively introduced at the α-position to the carbonyl group in the 6-membered ring in high yield. The regioselective introduction of the olefin moiety could be envisaged to proceed through a Mannich-type reaction involving the aminomethylating agent 24, which, in turn, is generated in situ by the action of HMDS on MOMCl.
Metal-Free Transfer Hydrobromination of C–C Triple Bonds
作者:Weiqiang Chen、Martin Oestreich
DOI:10.1021/acs.orglett.9b01431
日期:2019.6.21
A transfer hydrobromination of C–C triplebonds inititated by Brønsted acids is reported. Hydrogen bromide is released stepwise from a bench-stable cyclohexa-1,4-diene-based surrogate, generating biphenyl and ethylene as waste. A range of vinyl bromides was prepared from terminal and internal, mainly acceptor-substituted alkynes with good functional-group tolerance.
An aldehyde with a cyclohexa‐2,5‐dienyl group in the α‐position is introduced as a storable surrogate of highly reactive acetaldehyde. The cyclohexa‐2,5‐dienyl unit is compatible with an enantioselective Michael addition to nitroalkenes promoted by a Hayashi–Jørgensen catalyst and can be removed by a boron Lewis acid mediated C−C bond cleavage. The robust two‐step sequence does not require a large