Gold-Catalyzed [5,5]-Rearrangement

A highly
efficient gold-catalyzed cycloisomerization of 1,5-diynes
was developed. Various functional groups are tolerated under the mild
reaction conditions, which provides an alternative approach for the
synthesis of indeno­[1,2-c]­furans. On the basis of
mechanistic studies, including crossover experiments, deuterium labeling,
and computational chemistry, the product formation proceeds via a
formal [5,5]-sigmatropic rearrangement, a yet unknown reactivity pattern
in gold catalysis. Instead of a synchronous concerted [5,5]-sigmatropic
rearrangement and beyond an asynchronous concerted mode, each involving
a single transition state, two energetically low transition states
(1.8 and 5.6 kJ/mol) and an intermediate associate of the migrating
benzyl cation and the vinyl gold species could be located in the computations.

本研究开发了一种高效的金催化1,5-二炔环异构化反应。该反应在温和的反应条件下可兼容多种官能团，为茚并[1,2-c]呋喃的合成提供了一条替代路径。基于交叉实验、氘标记以及计算化学等机理研究结果，该产物的生成经由形式上的[5,5]-σ重排过程——这一金催化领域尚未见报道的反应模式。与仅涉及单一过渡态的协同同步[5,5]-σ重排及异步协同模式均不同，计算结果中可观测到两个低能过渡态（能垒分别为1.8和5.6 kJ/mol），以及一个由迁移苄基阳离子与乙烯基金物种构成的中间体缔合体。