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Catalytic Synthesis of Cyclic Guanidines via Hydrogen Atom Transfer and Radical-Polar Crossover

Cyclic guanidines are found in many biologically active compounds and natural products. Further, the for-mation of the atypical 7-membered ring of cyclic guanidine remains challenging due to a lack of efficient preparation strategies and low yield. Herein, a catalytic synthetic method for cyclic guanidines was developed via transition-metal hydrogen atom transfer and radical-polar crossover. This mild and functional-group tolerant process enabled the cycliza-tion of an alkenyl guanidines bearing common protective groups, such as Cbz and Boc groups. This powerful method not only provided typical 5- and 6-membered rings but also the atypical 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the selective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatizations.