瑞士洛桑联邦理工学院Waser Jrme团队报道了通过氧化还原金催化获得难以捉摸的σ型环丙烯阳离子等价物。相关研究成果于2024年5月23日发表于国际顶尖学术期刊《自然—化学》。

环丙烯是最小的不饱和碳环。从环丙烯中去除一个取代基会产生环丙烯阳离子（C₃₊系统，CPCs）。1957年，Breslow通过去除脂肪族位置上的取代基发现了稳定的芳香π型CPCs。相比之下，通过去除烯烃上的一个取代基而正式获得的σ型CPCs是不稳定的，并且相对未被探索。

该文中，研究人员介绍了亲电环丙烯基金（III）物种作为σ-型CPCs的等价物，可以与末端炔烃和乙烯基硼酸反应。在催化剂负载量低至2mol%的情况下，高度官能化的炔基或烯基环丙烯的合成在温和的条件下进行。一类高价碘试剂——环丙烯基联碘氧化物（CpBX）——能够将金（I）直接氧化为金（III），同时转移环丙烯基。该方案是通用的，对许多官能团具有耐受性，可用于复杂天然产物、生物活性分子和药物的后期修饰。

附：英文原文

Title: Accessing elusive σ-type cyclopropenium cation equivalents through redox gold catalysis

Author: Li, Xiangdong, Wodrich, Matthew D., Waser, Jrme

Issue&Volume: 2024-05-23

Abstract: Cyclopropenes are the smallest unsaturated carbocycles. Removing one substituent from cyclopropenes leads to cyclopropenium cations (C3+ systems, CPCs). Stable aromatic π-type CPCs were discovered by Breslow in 1957 by removing a substituent on the aliphatic position. In contrast, σ-type CPCs—formally accessed by removing one substituent on the alkene—are unstable and relatively unexplored. Here we introduce electrophilic cyclopropenyl-gold(III) species as equivalents of σ-type CPCs, which can then react with terminal alkynes and vinylboronic acids. With catalyst loadings as low as 2mol%, the synthesis of highly functionalized alkynyl- or alkenyl-cyclopropenes proceeded under mild conditions. A class of hypervalent iodine reagents—the cyclopropenyl benziodoxoles (CpBXs)—enabled the direct oxidation of gold(I) to gold(III) with concomitant transfer of a cyclopropenyl group. This protocol was general, tolerant to numerous functional groups and could be used for the late-stage modification of complex natural products, bioactive molecules and pharmaceuticals.

DOI: 10.1038/s41557-024-01535-8

Source: https://www.nature.com/articles/s41557-024-01535-8