Coordination-Induced Stereocontrol over Carbocations: Asymmetric Reductive Deoxygenation of Racemic Tertiary Alcohols
作者:Mayuko Isomura、David A. Petrone、Erick M. Carreira
DOI:10.1021/jacs.9b00862
日期:2019.3.20
intermediate tertiary carbocations. This approach has been implemented to achieve the first example of enantioselective reductive deoxygenation of tertiaryalcohols. This reduction occurs with high enantio- (up to 96% ee) and regioselectivity (up to >50:1 rr) by applying a novel Hantzsch ester analogue as a convenient hydride source. In-depth mechanistic studies support the involvement of a tertiary carbocation
limited to the construction of tertiarychiralcenters. The asymmetric generation of acyclic products containing all-carbon quaternary stereocenters from substituted 1,3-dienes represents a more challenging, but highly desirable, synthetic process for which there are very few examples. Herein, we report the highly selective copper-catalyzed generation of chiral all-carbon acyclic quaternary stereocenters
Transition metal promoted reactions. 30. Cyclopropyl anion as an allyl anion synthon. Novel synthesis of butadienes by nickel-catalyzed coupling of cyclopropyl Grignard reagents with dithioacetals
作者:Dennis K. P. Ng、Tien Yau Luh
DOI:10.1021/ja00207a029
日期:1989.12
Resolution of the reaction mixture and isolation of the triester product can be accomplished by using HPLC (4.6 X 250 mm Hypersil-ODS with 0.02 M KH2P04, pH 5.5, and a methanol gradient). Modification of the phosphorothioate was observed to be more efficient for the single-stranded d[CGCA(s)AAAAAGCG] fragment than the self-complementary eicosomer, d[CGTACTAGTT(s)AACTAGTACG] . This difference in reactivity
反应混合物的拆分和三酯产物的分离可以通过使用HPLC(4.6 X 250 mm Hypersil-ODS,具有0.02 M KH 2 PO 4 ,pH 5.5和甲醇梯度)来完成。观察到硫代磷酸酯的修饰对于单链 d[CGCA(s)AAAAAGCG] 片段比自身互补的低分子异构体 d[CGTACTAGTT(s)AACTAGTACG] 更有效。当反应混合物在 50 ℃加热时,这种反应性差异被部分克服。在不存在硫代磷酸二酯的情况下,使用天然寡脱氧核苷酸的对照反应不会产生任何显着的标记。'2未标记的十二聚体螺旋,d [CGCA(s) AAAAAGCG].d[CGCTTTTTTGCG],表现出的 T 为 55" C,这与 T 无法区分,PROXYL 标记(图 1 中的 a)或药物标记(图 1 中的 b)螺旋获得的值。与未标记的片段(T ,= 67”C)相比,具有两个标记的自身互补的ε-异构体 d[CG
Cyclopropylmethyl Palladium Species from Carbene Migratory Insertion: New Routes to 1,3-Butadienes
作者:Lei Zhou、Fei Ye、Yan Zhang、Jianbo Wang
DOI:10.1021/ol2034405
日期:2012.2.3
Cyclopropylmethyl palladium species can be accessed by Pd-catalyzed reaction of either cyclopropyl N-tosylhydrazone with halide or N-tosylhydrazone with cyclopropyl halide. In both approaches migratory insertion of Pd carbene is the key process. These transformations constitute new approaches toward 1,3-butadiene derivatives.