An Organic EnT Photocatalyst 4CzMeBN and the Application in the Synthesis of cis‐Fused Azetidines.

A powerful EnT photocatalyst 4CzMeBN has been developed and utilized in the synthesis of <italic>cis</italic>‐fused azetidines <italic>via</italic> dearomative [2+2] cycloaddition under visible light. The photocatalyst 4CzMeBN is a donor‐acceptor cyanoarene and features high triplet state energy and long lifetime of triplet state, which would be an alternative to widely used EnT photocatalyst Ir[dF(CF3)ppy]2(dtbbpy)PF6. The photochemical [2+2] cycloaddition provides a facile method to synthesize valuable dihydroisoquinolone‐fused azetidines with high efficiency. [ABSTRACT FROM AUTHOR]