Two-Step, One-Pot Synthesis of Visible-Light-Responsive 6‑Azopurines

The first general two-step, one-pot synthetic route to 6-azopurines is presented. Microwave-assisted nucleophilic aromatic substitution of protected 6-chloropurines with hydrazines or hydrazides, followed by metal-free oxidation with oxygen, gives 6-azopurines in high to excellent yields. Photophysical studies revealed intensive n−π* absorption band that makes trans-to-cis photoswitching possible using visible light (λ = 530 nm).