Controlled Reactivity of 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU) in the Selective Synthesis of 1‐(Bromoethynyl)arenes

The nucleophilic reactivity of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) was completely controlled by the formation of monohydrate (DBU⋅H2O) in the synthesis of 1‐(bromoethynyl)arenes from 1,1‐dibromoalkenes. Differential reactivity of DBU in protic solvents as compared to aprotic solvents has been explored to prevent the formation of mixtures of products in this reaction. Hydrated DBU is found to be superior to dry DBU, both for the selective synthesis and ease of isolation. In addition, use of DBU⋅H2O as a non‐nucleophilic mild base allowed us to synthesise 1‐(bromoethynyl)arenes via a reaction under solvent‐free conditions. Utilization of DBU⋅H2O as sole reagent also allowed us to isolate the products without column chromatographic purifications.