Lewis Base Catalyzed, Enantioselective Aldol Addition of Methyl Trichlorosilyl Ketene Acetal to Ketones
作者:Scott E. Denmark、Yu Fan、Martin D. Eastgate
DOI:10.1021/jo0506276
日期:2005.6.1
addition of an acetate enolate equivalent to ketones is described. Methyl trichlorosilyl ketene acetal reacts with a wide range of ketones in the presence of pyridine N-oxide to afford the aldol addition products in excellent yields. Chiral 2,2‘-pyridyl bis-N-oxides bearing various substituents at the 3,3‘- and 6,6‘-positions also provide excellent yields of the aldolproducts with variable enantioselectivities
Catalytic, Enantioselective Aldol Additions to Ketones
作者:Scott E. Denmark、Yu Fan
DOI:10.1021/ja025670e
日期:2002.4.1
(possessing both axial and central chiral elements) the aldol addition takes place again in excellent yield and with good stereoselectivity. The enantioselectivities of the additions are highly variable (7-86% ee) and are strongly dependent on the structure of the ketone acceptor. Aromatic methylketones gave the highest selectivity, whereas olefinic ketones were the least selective.
已经证明了三氯甲硅烷基乙烯酮缩醛对酮的催化、对映选择性加成。在催化量的吡啶 N-氧化物存在下,乙酸甲酯的三氯甲硅烷基烯醇化物与多种酮(芳香族、烯烃、炔属、脂肪族)发生快速和高产率的羟醛加成反应。此外,在催化量(10 mol%)的手性双吡啶双 N 氧化物(具有轴性和中心手性元素)存在下,醛醇加成再次以优异的产率和良好的立体选择性发生。添加物的对映选择性变化很大(7-86% ee)并且强烈依赖于酮受体的结构。芳族甲基酮的选择性最高,而烯酮的选择性最低。
Unprecedented C-6 functionalisation of 3-picoline induced by a methyl to C-6 lithium shift
作者:Julien Mathieu、Philippe Gros、Yves Fort
DOI:10.1039/b001690j
日期:——
BuLi–Me2N(CH2)2OLi
(BuLi–LiDMAE) promoted the clean C-6 functionalisation of 3-picoline
via a methyl to C-6 lithium shift.
Synthesis and Characterization of Aluminum Complexes of Redox-Active Pyridyl Nitroxide Ligands
作者:Andrew M. Poitras、Justin A. Bogart、Bren E. Cole、Patrick J. Carroll、Eric J. Schelter、Christopher R. Graves
DOI:10.1021/acs.inorgchem.5b01941
日期:2015.11.16
The aluminum complexes ((R)pyNO(-))(2)AlCl ((R)pyNO(-) = N-tert-butyl-N-(2-pyridyl)nitroxyl; R = H (1), CH3 (2), CF3 (3)) were prepared in 80-98% yield through the protonolysis reaction between the pyridyl hydroxylamine ligand precursors (R)pyNOH and dimethylaluminum chloride. Complex 1 was also prepared using a salt metathesis route in 92% yield. Complexes 1-3 were characterized using H-1 and C-13 NMR spectroscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 1-3 are isostructural, with the Al-III cation in all cases being five coordinate with distorted square pyramidal geometries. The geometry of complex 1 was studied using DFT, which showed primarily ligand-based frontier molecular orbitals. Reaction of 1 with NaOt-Bu gave (pyNO(-))(2)AlOt-Bu (4), while reaction of 1 with AgBPh4 gave [(pyNO(-))(2)Al(THF)(2)][BPh4] (5) in 54% and 87% yields, respectively. Compounds 4 and 5 were both characterized using H-1 and C-13 NMR spectroscopies and compound 5 by X-ray diffraction. Complexes 1-5 were also characterized by UV-vis electronic absorption spectroscopy and electrochemistry. The cyclic voltammograms of the complexes show two separate oxidation process, the potentials of which are dependent on both the substitution pattern of the (R)pyNO(-) ligands and the anion that completes the aluminum coordination sphere. A correlation was determined between the chemical shift of the t-Bu of the (R)pyNO(-) ligand in the H-1 NMR spectroscopy and the potentials of the redox events for complexes 1-4.
Preparation of chiral bipyridine bis-N-oxides by oxidative dimerization of chiral pyridine N-oxides
作者:Scott E. Denmark、Yu Fan
DOI:10.1016/j.tetasy.2005.12.039
日期:2006.2
The direct preparation of chiral 2,2′-bipyridine bis-N-oxides has been developed. The method involves two stages, first, the deprotonation of substituted chiral pyridine N-oxides and second, the oxidative dimerization of the resulting 2-lithiopyridine N-oxides. Optimization of the reaction conditions led to the selection of LiTMP in THF for the deprotonation and molecular iodine as the oxidant. The