A facile synthesis of 2-ethynylpyrroles by ButOK-assisted room temperature deprotection of 2-(acylethynyl)pyrroles

Available N-substituted 2-(acylethynyl)pyrroles undergo room temperature deprotection in the Bu^tOK/THF system to give 2-ethynylpyrroles in 82–92% yields. Quantum-chemical calculations (B2PLYP/6-311G**//B3LYP/6-311G**+C-PCM/THF) show that the cleavage of ethynyl–acyl bond via the proton transfer from Bu^tOK with formation of potassium acylate and 2-methylpropene is thermo-dynamically much more preferred compared to alternative nucleophilic attack of tert-butoxide anion at the acyl carbon (ΔG = –35.1 vs. –2.7 kcal mol^-1).