Cuprous Chloride Accelerated Stille Reactions. A General and Effective Coupling System for Sterically Congested Substrates and for Enantioselective Synthesis
作者:Xiaojun Han、Brian M. Stoltz、E. J. Corey
DOI:10.1021/ja991500z
日期:1999.8.1
of cuprous chloride as an accelerant for coupling. Thus, using a protocol for coupling that involves the system Pd(PPh3)4/CuCl/LiCl under anaerobic conditions in dimethylsulfoxidesolution at 60 °C, a wide variety of Stille coupling reactions which otherwise fail can be effected in excellent yield (Table 1). The process has been applied to the enantioselective synthesis of the chiral 1-(arylethyl)alkylcarbinol
Stille 偶联反应的一个主要限制来自空间筛选,特别是在乙烯基锡烷组分中。例如,由于非常缓慢的反应速率和竞争性电影取代,通常观察到 1-取代的乙烯基锡烷和芳基全氟烷烃磺酸盐或卤化物可以忽略不计或低产率。通过发现和应用氯化亚铜作为偶联促进剂,这个问题在目前的工作中得到了克服。因此,使用涉及 Pd(PPh3)4/CuCl/LiCl 系统在 60 °C 的二甲基亚砜溶液中的厌氧条件下的耦合协议,可以以优异的产率实现各种各样的 Stille 耦合反应,否则这些反应会失败(表1)。该工艺已应用于手性1-(芳乙基)烷基甲醇26的对映选择性合成,天然产物尼康酮的模型。氯化亚铜对Stille偶联的加速可以通过乙烯基锡烷→乙烯基铜(I)跨金属的干预来解释。
Divergent Regioselectivity in the Synthesis of Trisubstituted Allylic Alcohols by Nickel- and Ruthenium-Catalyzed Alkyne Hydrohydroxymethylation with Formaldehyde
作者:Cory C. Bausch、Ryan L. Patman、Bernhard Breit、Michael J. Krische
DOI:10.1002/anie.201101496
日期:2011.6.14
Stoichiometric metals banned: Nonsymmetrically disubstituted alkynes were converted into primary trisubstitutedallylicalcohols upon exposure to paraformaldehyde in the presence of nickel or ruthenium catalysts, which exhibit complementary regioselectivity and complete stereoselectivity in the absence of exogenous reducing agents (see scheme).
Stille coupling versus cine substitution. Electronic effects also influence coupling sterically hindered stannanes
作者:Alexander Flohr
DOI:10.1016/s0040-4039(98)01058-2
日期:1998.7
electropholes allow Stille couplings to very hindered stannanes, not possible under common conditions. In contrast, the usage of triflates and elevated temperatures yields exclusively the product of a Cine substitution. In this was, by the choice of the reaction conditions, two alternative stereoisomers can be obtained from the same stannane.
An Antibody-Catalyzed Allylic Sulfoxide−Sulfenate Rearrangement
作者:Zhaohui S. Zhou、Alexander Flohr、Donald Hilvert
DOI:10.1021/jo991299a
日期:1999.10.1
whereas specific conformational constraints programmed by the haptens must orient the flexible substrate within the induced antibody-combining sites so as to favor certain reaction pathways over others. These studies thus expand the scope of antibody catalysis to an important new class of pericyclic reactions and illustrate how medium effects can be exploited together with conformational constraint to
Irradiation of a bichromophoric 1-(o-cyanobenzyloxy)-2-(p-methoxyphenyl)-2-butene (1a) in cyclohexane gave an isoquinoline derivative, 8-methoxy-6-methyl-11,13-dihydro[2]benzoxepino[5,4-c]isoquinoline (2a). The structure was determined by X-ray analysis. The formation of 2a can be accounted for by the initial cycloaddition of 1a in the excited singlet state between the C=C double bond and C≡N triple bond, followed by cleavage of the resulting azetine ring and recyclization.