Visible-Light-Promoted Access to Fused Aza-Heterocyclic Frameworks

The development of innovative and sustainable synthetic methodologies is crucial to address the increasing demand for environmentally benign practices in all domains of organic chemistry. In this regard, harnessing visible light as the sole energy input is particularly attractive. Diazo compounds, being highly versatile reagents with notable reactivity and ready accessibility, are well-suited for photochemical activation, which offers a promising, eco-friendly alternative to traditional transition-metal-catalyzed processes. In this perspective, we report generalized photochemical pathways for the synthesis of benzene fused 1,4- and 1,3-diazines from 1,4- and 1,5-aza bis-nucleophiles and various diazo compounds, employing water as the sole and distinct solvent under aerobic presence. These protocols involve the direct photoinduced generation of carbenes from diazo compounds, averting the need of any photocatalyst, which then opts [4+2] or [5+1]-annulation pathway and offers distinct products. The detailed insights into the reaction pathways are investigated through several control experiments and DFT studies. Strategically it is also possible to construct a 5-membered aza-heterocyclic core applying the same photochemical approach. Finally, the late-stage modifications of quinoxalinone and quinoxaline scaffold applying the photoinduced C-H activation technique generate the structurally diverse spiroindene compounds, including steroid-embedded di-aza heterocycle.