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。从环丙烯中除去一个取代基会产生环丙烯鎓阳离子（C ₃ ⁺系统，CPC）。 Breslow于1957年通过去除脂肪族位置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而获得）不稳定且相对未经探索。在这里，我们引入亲电子环丙烯基金（III）物质作为σ型CPC的等价物，然后它可以与末端炔烃和乙烯基硼酸反应。催化剂负载量低至 2 mol%，高度官能化的炔基或烯基环丙烯的合成在温和条件下进行。一类高价碘试剂——环丙烯基苯并氧杂环戊烯 (CpBXs)——能够将金 (I) 直接氧化为金 (III)，并同时转移环丙烯基。该方案具有通用性，对多种官能团具有耐受性，可用于复杂天然产物、生物活性分子和药物的后期修饰。