Diastereoselective 1,3-Dipolar Cycloaddition of 2-(a,b-Unsaturated) Acyl-3-phenyl-l-menthopyrazoles
摘要:
The 1,3-dipolar cycloadducts of N-(alpha,beta-unsaturated) acylpyrazoles (2) with benzonitrile oxide or nitrones were afforded in good yield. in the cases of nitrones, the addition of MgBr2 or ZnBr2 promoted the stereoselectivity as well as the acceleration of the reaction rate. In the reaction of 2f and 2g, the big jump on the diastereoselectivity was accomplished by the addition of MgBr2, and (3'S,4'R,5'S)-8 was obtained as optically pure form in over 90% yield. These isoxazolidinecarbonylpyrazoles were converted into azetidinones in moderate yield with the retention of their stereo structures.
Catalytic, Enantioselective Addition of Alkyl Radicals to Alkenes via Visible-Light-Activated Photoredox Catalysis with a Chiral Rhodium Complex
作者:Haohua Huo、Klaus Harms、Eric Meggers
DOI:10.1021/jacs.6b03399
日期:2016.6.8
An efficient enantioselective addition of alkyl radicals, oxidatively generated from organotrifluoroborates, to acceptor-substituted alkenes is catalyzed by a bis-cyclometalated rhodium catalyst (4 mol %) under photoredox conditions. The practical method provides yields up to 97% with excellent enantioselectivities up to 99% ee and can be classified as a redox neutral, electron-transfer-catalyzed reaction
An enantioselective sulfa‐Michael‐cyclization reaction was developed for the synthesis of 1,5‐benzothiazepines with versatile pharmacological activities. The reaction between 2‐aminothiophenol and α,β‐unsaturated pyrazoleamides gave direct access to N−H‐free 1,5‐benzothiazepines in the presence of a chiral N,N′‐dioxide/Yb(OTf)3 complex. Excellent enantioselectivities (up to 96 % ee) and high yields
Asymmetric conjugate hydrocyanation of α,β-unsaturated carboxylic acid derivatives catalyzed by a Ru[(S)-phgly]2[(S)-binap]–CH3OLi system was examined. The N-acylpyrrole gave the best result in terms of reactivity and enantioselectivity. A series of substrates with alkyl or heterosubstituted alkyl groups at the β-position reacted with a substrate-to-catalyst molar ratio of 200–2000 to afford the β-cyano
effective asymmetriccatalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated
Magnesium Complexes as Highly Effective Catalysts for Conjugate Cyanation of α,β-Unsaturated Amides and Ketones
作者:Jinlong Zhang、Xihong Liu、Rui Wang
DOI:10.1002/chem.201304835
日期:2014.4.22
Asymmetric cyanation of trimethylsilyl cyanide (TMSCN) with α,β‐unsaturated amides and ketones, respectively, catalyzed by bifunctional mononuclear 1,1′‐bi‐2‐naphthol (BINOL)–Mg and binuclear bis(prophenol)–Mg catalysts was realized. A series of synthetically important 1,4‐cyano products were obtained with good to high enantioselectivities (up to 97 % ee).