Photoinduced [3+2] Cycloaddition of Alkyl–Acceptor Diazoalkanes: Diversity-Oriented Synthesis of Pyrazolines Containing a Quaternary Center

We present a new [3+2] cycloaddition reaction between alkyl–acceptor diazoalkanes under visible light irradiation. By employing easily accessible alkyl–acceptor-type diazoalkanes or their precursor hydrazones as both 1,3-dipoles and dipolarophiles, a diverse range of pyrazoline derivatives featuring a quaternary center have been efficiently synthesized in a predictable manner, with excellent functional group tolerance and good yields. Furthermore, scale-up experiments and downstream transformations of the product were also detailed.