Ring Opening of 3‐Bromo‐2‐Isoxazolines to β‐Hydroxy Nitriles
摘要:
3-Bromo-2-isoxazolines were converted to the corresponding beta-hydroxy nitriles by treatment with sodium iodide in the presence of either chlorotrimethylsilane or para-toluenesulfonic acid. Both methods gave beta-hydroxy nitriles under relatively mild conditions in good to moderate yields for a variety of substituted 3-bromo-2-isoxazolines.
Gold(III) Chloride-Catalyzed Diastereoselective Alkylation Reactions with Chiral Benzylic Acetates
作者:Philipp Rubenbauer、Thorsten Bach
DOI:10.1002/adsc.200700600
日期:2008.5.5
Gold(III) chloride was shown to be an efficient catalyst for the diastereoselective CC bond formation of various chiral para-methoxybenzylic acetates and different nucleophiles. All electrophilic acetates carried next to the reacting center a stereogenic carbon center bound to a functional group (FG), a methyl substituent and a proton. Selectivities were good (dr>80/20) in favor of the anti-product
氯化金(III)被证明是形成各种手性对甲氧基苄基乙酸酯和不同亲核试剂的非对映选择性CC键的有效催化剂。所有亲电子的乙酸酯在反应中心附近均带有与官能团(FG),甲基取代基和质子键合的立体碳中心。选择性好(dr > 80/20),对于FG = COOMe,NO 2和CN有利于产生反产物,对于FG = SO 2 Et,PO(OEt)2有利于合成产物。反应最有可能通过一种游离碳正离子,其中优选的构象可促进面部分化。几种芳烃亲核试剂显示与催化条件兼容,可提供高收率的相应取代产物(13个实例,占62-98%)。此外,其他亲核试剂(烯丙基三甲基硅烷,三甲基甲硅烷基氰化物,2,2-二甲基-3-(三甲基甲硅烷基氧基)丁烷,对甲苯磺酰胺和乙酰丙酮)与代表性手性亲电子试剂以高产率和非对映选择性的方式反应。
Precursors 5-7 of chiral para-methoxybenzyl cations (2-4), which carry a polar substituent (NO2, CN, OH) at the stereogenic α-carbon atom, reacted under acidic conditions with high facial diastereoselectivity (dr = 75:25 to >95:5) to the corresponding 1,1-diarylalkanes threo-9 (50-87% yield). Catalytic amounts of Sc(OTf)3 as Lewis acid were sufficient to convert epoxide 7 into the corresponding alcohols threo-9ca and threo-9cb.
A convenient and facile stereoselectivesynthesis of (E)- and (Z)-trisubstituted alkenes has been achieved by treatment of unactivated Baylis–Hillmanadducts with NaBH4 in the presence of CuCl2·2H2O at room temperature for 15 min.
Chiral Benzylic Carbocations: Low-Temperature NMR Studies and Theoretical Calculations
作者:Daniel Stadler、Alain Goeppert、Golam Rasul、George A. Olah、G. K. Surya Prakash、Thorsten Bach
DOI:10.1021/jo802296e
日期:2009.1.2
delivering high diastereomeric ratios, supporting the hypothesis that these carbocations are involved as intermediates in previously studied SN1reactions. A strong shielding effect at the benzylic carbocationic center is observed for most of the secondarybenzylic carbocations (derived from precursors 5−13) investigated, indicating a strong mesomeric distribution of the positive charge to the carbon
α-手性仲和叔碳阳离子苄19 - 30,从相应的苄醇产生的1,2,和5 - 14通过用FSO 3 H或FSO 3 H /的SbF 5在SO 2ClF在-70°C下作为溶剂,并通过一维和二维NMR光谱进行表征。偶合常数和NOESY测量结果表明一种优选的构型,其中α-氢原子占据1,3-烯丙基应变位置,阳离子的非对映异构面通过烷基取代基和官能团(FG)区分。通过使用B3LYP / 6-311 + G **级别的DFT方法进行计算,进一步支持了这种优选构象的存在。芳烃亲核体的淬灭实验显示,受到较低屏蔽的非对映异构体表面的优先攻击,从而提供了高非对映异构体比率,支持了以下假说:这些碳正离子作为中间体参与了先前研究的S N中1反应。对于大多数次级苄碳正离子(来自前体衍生的,观察到在苄基碳阳离子中心的强的屏蔽效果5 - 13)研究,表明在茴香基取代基的对位上的正电荷的强消旋分布的碳原子。对于α-卤素取代的碳阳离子(5
Interfacial tuning of electrocatalytic Ag surfaces for fragment-based electrophile coupling
of C‒C bonds in medicinal chemistry frequently draws on the reductivecoupling of organic halides with ketones or aldehydes. Catalytic C(sp3)‒C(sp3) bond formation, however, is constrained by the competitive side reactivity of radical intermediates following sp3 organic halide activation. Here, an alternative model deploys catalytic Ag surfaces for reductive fragment-based electrophile coupling compatible