Triarylamminium Radical Cation Facilitates the Deprotection oftert-Butyl Groups in Esters, Ethers, Carbonates, and Carbamates

Abstract

We report a catalytic protocol for mild OtBu deprotection using two commercial reagents: the tris-4-bromophenylamminium radical cation, commonly known as magic blue (MB •+ ), and triethylsilane. Magic blue catalytically facilitates the cleavage of the C−O bond in tert-butyl carbamates, carbonates, esters, and ethers in a high isolated yield of up to 95%, and sacrificial triethylsilane accelerates the reaction. Without requiring high temperatures, transition metals, or strong acidic or basic catalysts, this method is suitable for structurally diverse compounds, including aliphatic, aromatic, and heterocyclic substrates.

Structure–property–function relationships of stabilized and persistent C- and N-based triaryl radicals

“…MB is reasonably stable but known to slowly decompose upon storage in solid state and to abstract hydrogen atoms from organic solvents, decomposing to the corresponding triarylamine. 62 In a study of aged commercial MB samples, the tetrakis-(4-bromophenyl)benzidine (TPB) radical cation and its dication were the main decomposition products and thus termed “blues brothers”. 63 The instability of MB was explained by the weak C–Br bond in the para -position that cleaves and enables benzidine coupling.…”