Cyclisation reactions have always drawn the attention of organic chemists in pursuit of methods for the selective construction of natural‐product‐like polycyclic compounds. The search for new and efficient ring‐forming reactions has witnessed growing interest, resulting in the design of many elegant synthetic strategies and the discovery of useful methodologies. In this context, cycloisomerisation reactions are very attractive, because they allow for the rapid generation of molecular complexity with use of a low loading of a promoter, thus limiting waste production. The search for sustainable and more efficient catalytic systems remains challenging. Relatively nontoxic and inexpensive bismuth(III) salts are of particular interest for catalytic organic synthesis. More specifically, the highly active triflate salt is known to be noncorrosive and easy to handle. This microreview focuses on cyclisation reactions assisted by bismuth(III) triflate catalysis.

The cycloisomerization of allene-enol ethers under Bi(OTf)3 catalysis was developed as a novel "atom-economic" tool for accessing interesting functionalized cyclopentene rings. Bi(OTf)3 was shown to promote selectively the activation of the enol ether moiety of the substrate. This catalytic methodology was further extended to the synthesis of dihydrofuran and oxaspirocycle derivatives.