K2CO3-Mediated Intramolecular Oxa-Michael Cyclization of α,β-Unsaturated Ketoximes: Synthesis of Densely Arene-Substituted 2-Isoxazolines Bearing a Quaternary Center
Synthesis of trifluoromethyl-/cyclopropyl-substituted 2-isoxazolines by DBU-promoted domino reaction
作者:Xiao-Dong Liu、Hai-Yan Ma、Chun-Hui Xing、Long Lu
DOI:10.1016/j.cclet.2017.03.031
日期:2017.8
cyclopropyl substituted 2-isoxazolines were synthesized via a DBU-promoted domino reaction of β-trifluoromethyl-/β-cyclopropyl-substituted enones with hydroxylamine. The domino reaction consists of a Michael addition and the followed cyclization. A wide range of 3-substituted 5-cyclopropyl-5- trifluoromethyl-2-isoxazolines were obtained in good to excellent yields under mild reaction conditions. The method
Cuts both ways: The title reaction consists of an addition/cyclization/dehydration sequence and affords the biologically important chiral 3,5‐diaryl‐5‐(trifluoromethyl)‐2‐isoxazolines 1 in excellent yields with high ee values. The flexibility of accessing either the S or R enantiomers of the products has been achieved by the appropriate choice of phase‐transfer catalyst (2).
It all adds up: The activation of aromatic isoxazoles with a nitro group at the 4‐position has enabled the first regio‐ and diastereoselective trifluoromethylation at the 5‐position of isoxazoles by nucleophilic addition using Me3SiCF3 (see scheme; DMF=N,N′‐dimethylformamide). The process was demonstrated with a broad range of 3,5‐aromatic, heteroaromatic and aliphatic substrates.
所有这些加起来:在4位上带有硝基的芳香异恶唑的活化,使得能够通过Me 3 SiCF 3的亲核加成在异恶唑的5位上进行第一次区域和非对映选择性的三氟甲基化(参见方案; DMF = N ,N'-二甲基甲酰胺)。广泛的3,5-芳族,杂芳族和脂族底物都证明了该方法。