Diazines-to-Diazoles Skeletal Remodeling

Nitrogen-containing heteroarenes, particularly diazines (six-membered dinitrogen aromatics) and diazoles (five-membered dinitrogen aromatics), constitute the bedrock of modern pharmaceutical and agrochemical architectures. Synthetic capability to edit these heteroaromatic scaffolds through precise core-atom transformations opens the door to previously untapped chemical spaces, thus accelerating discovery campaigns for developing pharmaceutical drugs and agrochemicals. Here we report a photocatalytic platform for the skeletal remodeling of diazines into diazoles, encompassing three distinct permutations: conversion of pyrimidines (1,3-diazines) to imidazoles (1,3-diazoles), and pyridazines (1,2-diazines) to pyrazoles (1,2-diazoles) facilitated by formal ring contractions that proceed via either rehybridizative transposition or deletion of an aromatic carbon unit. Key to this strategy is harnessing photocatalytic single-electron transfer (SET) to access dearomatized diazacyclohexadienyl anions, which undergo precisely orchestrated ring contraction via disrotatory 6π-1,5-electrocyclization.