Improving the Photochemical Skeletal Enlargement of Pyridines to 1,2-Diazepines with Isocyanates

In this work, we extend the one-pot protocol to synthesize 1,2-diazepines from commercially available and cheap starting materials. Capitalizing on isocyanate derivatives as activating agents, the photochemical skeletal enlargement occurs, while preserving key functional groups embedded in more than 30 substrates. We also demonstrated that isocyanates can be generated in situ exploiting the wealth of methods starting from bench stable resources. Compare to previous strategies, the use of these precursors prevents the presence of deleterious HCl traces in the system, thus enabling the synthesis of 1,2-diazepines in high yields over up to 5 sequential steps.