A full account on rhodium‐catalyzed asymmetric, directed hydroboration of functionalized prochiral cyclopropenes affording enantiomerically enriched cyclopropylboronates is reported. The scope and limitations of two alternate directing groups, ester and carboxamide, are evaluated. It was found that hydroboration of esters appeared to be more sensitive to substitution in the aromatic ring of the substrates
Simple Large-Scale Preparation of 3,3-Disubstituted Cyclopropenes: Easy Access to Stereodefined Cyclopropylmetals via Transition Metal-Catalyzed Hydrometalation
作者:Vladimir Gevorgyan、Michael Rubin
DOI:10.1055/s-2003-44368
日期:——
3-Disubstituted cyclopropenes have been readily prepared in a multigram scale via two different methods: (1) dehydrohalogenation of bromocyclopropanes, and (2) Rh-catalyzed addition of carbenoids to trimethylsilylacetylene followed by desilylation. Highly diastereoselective Pd-catalyzed hydrostannation and highly enantioselective Rh-catalyzed hydroboration of 3,3-disubstituted cyclopropenes afforded useful
explored by control experiments, providing a number of key insights. The kinetic process followed by 1H NMR indicated that the reaction was finished in 15 min. Furthermore, the mechanism of silver(I)-catalyzed hydroborylation of cyclopropenes was proposed, with the protonation by methanol as the rate-determining step.
在环丙烯与 B 2 pin 2的氢硼化中开发了一种有效的 (NHC)AgCl 催化,以立体选择性方式产生各种环吡基硼酸酯,可以轻松地转化为通用环丙烷的构建。该方案在露天气氛中的温和反应条件下有效地发挥作用,并且很容易在克规模上应用。这种新颖的方法还通过对照实验进行了详细探索,提供了许多关键见解。1 H NMR的动力学过程表明反应在 15 分钟内完成。此外,提出了银(I)催化环丙烯的硼氢化反应机理,其中甲醇质子化作为速率决定步骤。