[3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-b][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-b][1,2]oxazine Derivatives
作者:Yulia A. Antonova、Yulia V. Nelyubina、Sema L. Ioffe、Andrey A. Tabolin
DOI:10.3390/molecules28073025
日期:——
A rhodium(II)-catalyzed reaction of cyclic nitronates (5,6-dihydro-4H-1,2-oxazine N-oxides) with vinyl diazoacetates proceeds as a [3+3]-annulation producing bicyclic unsaturated nitroso acetals (4a,5,6,7-tetrahydro-2H-[1,2]oxazino[2,3-b][1,2]oxazines). Optimization of reaction conditions revealed the use of Rh(II) octanoate as the preferred catalyst in THF at room temperature, which allows the preparation
环状硝酸酯(5,6-二氢-4H-1,2-恶嗪 N-氧化物)与重氮基乙酸乙烯酯的铑 (II) 催化反应以 [3+3]-环化反应生成双环不饱和亚硝基缩醛 (4a, 5,6,7-四氢-2H-[1,2]恶嗪并[2,3-b][1,2]恶嗪)。反应条件的优化表明,在室温下使用辛酸 Rh(II) 作为 THF 中的首选催化剂,可以以良好的产率和出色的非对映选择性制备目标产物。在碱性条件下,即在DBU和醇的共同作用下,这些亚硝基缩醛通过不饱和恶嗪环收缩成相应的吡咯。这两种转化都可以以一锅法进行,因此构成了一种从可用的起始材料(如硝基烯烃、烯烃、