Peptide natural products have long served as inspiration for developing new therapeutics to treat human diseases. Therapeutic peptides commonly exhibit effective protein-target binding activity at low concentrations as a result of high selectivity and offer an inherent advantage of amino acid degradation products being minimally toxic. However, the value of peptide therapeutics is often overshadowed by a marked susceptibility to proteolytic degradation and subsequent failure to reach a validated target in vivo. The modification of bioactive linear peptides by cyclization has been shown to be an effective strategy for addressing this problem. In fact, the bioactivity and pharmacokinetic profiles of constrained cyclic peptides are often improved relative to their acyclic counterparts. Among Nature's wide range of peptide cyclization strategies, the oxidative coupling of aromatic amino acid sidechains has drawn considerable interest. Proteinogenic tyrosine (Tyr) residues are often involved in structure-altering oxidative cyclization events via the generation of tyrosyl radicals and related intermediates. Such redox active intermediates are notably involved in the formation dityrosine and isodityrosine protein crosslinks (Figure ). While these biaryl linkages are frequently identified as clinical markers of oxidative stress and aging, they have been shown to impart beneficial structural stability and elasticity to peptide and protein-based systems. Similar transformations are commonly observed in natural product biosynthesis pathways, resulting in structurally constrained monoand polycyclic peptides with promising and diverse biological activities. Exemplary biaryl-linked cyclic peptides that derive from phenolic-residue oxidation include the angiotensin-converting enzyme inhibitor, K-13 1 (C-O-linked), myxarylin 2 (C-N-linked), and C-Clinked antimicrobial peptides such as arylomycin A2 3 (Figure ). The desirable properties associated with cyclic peptides have motivated the development of creative synthetic methods to prepare cyclic peptides. Many of these strategies leverage the reactivity of free termini and residue side chain functionality, while others have introduced noncanonical residues to achieve site-selective cyclizations. Nature forms stable covalent linkages by using oxidative manifolds to impart structural rigidity and stability to proteolytic degradation. However, replicating the linkages formed in Tyr-and hydroxyphenylglycine (Hpg)-containing cyclic peptides with chemoselective control presents significant challenges. In view of their desirable properties, the need for developing efficient synthetic methodologies to access cyclic peptides is clear. Synthetic access to these types of linkages is often enabled through multistep approaches which use transition metal-catalyzed couplings (e.g., Suzuki couplings) or nucleophilic aromatic substitution as key reactions at residues with prefunctionalized phenolic side chains. Emerging residue-selective protein modification and labeling methods have shown great potential for the controlled functionalization of peptides. For example, Baran and coworkers recently reported a Cu-mediated oxidative phenol coupling to achieve scalable access to the biaryl-linked 14-atom macrocyclic core that is common to the arylomycins. Although transition metal-mediated strategies have enabled synthetic access to bioactive Tyr-linked cyclic peptides, few of these methods leverage the inherent nucleophilicity of phenolic side chains. Recently, synthetic and chemoenzymatic strategies for preparing related variations of this common macrocyclic core on scales suitable for manufacture were described by Gosselin and coworkers. However, the generality has not been demonstrated for peptides containing diverse amino acid residue functionality or extended beyond three residue precursors to access to larger biaryl-linked macrocycles. The underdeveloped reactivity of its phenolic side chain presents a novel platform to develop Tyr-selective peptide cyclization methods. Considering the need for such strategies, we drew inspiration from the simplicity of other oxidation-induced cyclizations that occur spontaneously under aerobic conditions for peptides containing multiple cysteine (Cys) residues, such as the facile conversion of 4 into vasopressin 5, and enzymatically, such as the remarkable conversion of 6 into C-C bond linked cyclic peptide 7. Given the prevalence of Tyr-linked cyclic peptide natural products, we set out to develop a method for the oxidatively-induced cyclization of Tyr-containing peptides.