The inert carbon–carbon bonds of aromatic systems have long impeded the direct diversification of phenolic feedstocks into value-added scaffolds. Although enzymatic or energy-intensive strategies enable limited arene modifications, the controlled and programmable ring opening of phenols to unlock both skeletal and functional group diversity remains a fundamental challenge. Here we report an operationally simple and efficient nitrogenation strategy for cleaving phenolic arene rings, converting phenols into uniquely structured acyclic N-containing products including cyanopenta-dienoates, cyanopenta-dienamides and cyanopenta-dienoic acids. The method also enables scaffold hopping of corresponding arene rings, leading to important five-, six- and seven-membered N-heterocycles. The strategy demonstrates broad utility in late-stage modification of bioactive molecules, diversified skeletal remodelling of phenolic feedstocks, and the application of ring-opening products in polymer development. This approach transforms phenols into programmable linchpins for accessing underexplored chemical space, offering broad potential for synthetic chemistry and materials science.