Diverse synthesis of bridged bicyclo[3.2.1]octa-2,6-diene and tricyclo[3.2.1.02,7] oct-3-ene frameworks via stepwise cascade reactions

Strained bridged rings bicyclo[3.2.1]octane and tricyclo[3.2.1.0^2,7]octane are prevalent in natural products known for their significant biological activities. However, strategies for efficiently synthesizing these complex frameworks from simple starting materials via de novo synthesis remain underexplored. This article presents an efficient strategy that combines phosphine catalysis and photocatalysis to execute a stepwise tandem reaction involving allenoates and α-cyano cinnamaldehydes, including [3 + 2] cyclization, [5 + 2] cyclization, acyl transfer, and decarboxylation reactions, synthesizing a series of functional bicyclo[3.2.1]octa-2,6-diene and tricyclo[3.2.1.0^2,7]oct‑3-ene skeleton derivatives with excellent chemoselectivity demonstrated throughout the process. Meanwhile, the reaction can also be performed via a one-pot, scalable phosphine/photocatalytic cascade process, efficiently yielding the bridged products which can serve as versatile intermediates for further applications.