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 2 mol%, 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.

环丙烯是最小的不饱和碳环。从环丙烯中去除一个取代基可得到环丙烯阳离子（C₃⁺ 系统，CPC）。1957 年，Breslow 通过去除脂肪族位点上的取代基发现了稳定的芳香族 π 型 CPC。相比之下，σ型 CPC（通过去除烯烃上的一个取代基正式获得）不稳定且相对未被探索。在这里，我们介绍了亲电环丙烯基金 （III） 物质作为 σ 型 CPC 的等价物，然后可以与末端炔烃和乙烯基硼酸反应。在催化剂负载量低至 2 mol% 的情况下，在温和条件下进行高度官能化的炔基或烯基环丙烯的合成。一类高价碘试剂——环丙烯基苯并氧唑 （CpBX）——能够直接将金 （I） 氧化成金 （III），同时发生环丙烯基团的转移。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。