A safe and fast method for the production of beta-hydroxy-alpha-diazoesters in continuous flow technology is described. The synthesis involves the formation of ethyl diazoacetate in situ and the addition to several aldehydes in a two-step continuous flow microreactor setup. Rhodium acetate catalyzes a subsequent 1,2-hydride shift to give access to beta-keto esters in a three-step sequence.
Lewis-Acid-Catalyzed Oxa-Michael Addition to Give α-Diazo-β-alkoxy Carbonyls and Tetrahydro-3<i>H</i>-furo[3,4-<i>c</i>]pyrazoles
作者:Avery M. Peck、Matthias Brewer
DOI:10.1021/acs.orglett.3c00723
日期:2023.4.21
The conjugate addition of alcohols to vinyl diazonium ions formed via Zn(OTf)2-catalysis gives α-diazo-β-alkoxy carbonyls. The diazo group is retained in this reaction, and this process is an efficient way to couple a reactive partner to the diazo fragment. As an example, we disclose that addition of allyl alcohols provides tetrahydro-3H-furo[3,4-c]pyrazoles via an addition/cycloaddition sequence.
醇与通过 Zn(OTf) 2催化形成的乙烯基重氮离子的共轭加成得到 α-重氮-β-烷氧基羰基。重氮基团保留在这个反应中,这个过程是将反应伙伴偶联到重氮片段的有效方法。例如,我们公开了添加烯丙醇可提供四氢-3 H -呋喃[3,4- c] 吡唑通过加成/环加成序列。这种两步顺序为这些空间位阻吡唑啉支架提供了良好的产率和良好的非对映选择性,具有多达三个四元中心和四个立体异构中心。这些产品在释放氮气后可以加工成环丙烷稠合四氢呋喃。反应条件温和,操作简单,避免使用昂贵的过渡金属催化剂。