2-Isopropylbenzimidazole and 2-methylbenzimidazole have been found to be effective bulky proton sources for stereoselective protonation of chiral enolate anions. 2-Isopropylbenzimidazole worked in the stereoselective protonation of the Birch reduction of chiral α,β-unsaturated imides. On the other hand, 2-methylbenzimidazole was found to be the best protonation reagent in the isomerization reaction of α,β-unsaturated imide into β,γ-unsaturated imide. The Birch reduction using 2-isopropylbenzimidazole realized a concise and stereoselective synthesis of δ-lactone 14, a sex pheromone of Macrocentrus grandii, while the isomerization reaction using 2-methylbenzimidazole was employed in the highly stereoselective synthesis of the γ-lactone intermediate in the synthesis of depsipeptide antibiotics. These bulky proton sources would be powerful tools to achieve a concise synthesis of natural products.

已经发现2-异丙基苯并咪唑和2-甲基苯并咪唑是手性烯醇酸根阴离子的立体选择性质子化的有效大体积质子源。2-异丙基苯并咪唑用于手性α，β-不饱和酰亚胺的桦木还原的立体选择性质子化。另一方面，在α，β-不饱和酰亚胺向β，γ-不饱和酰亚胺的异构化反应中，发现2-甲基苯并咪唑是最好的质子化试剂。使用2-异丙基苯并咪唑的桦木还原反应实现了δ-内酯14的简明和立体选择性合成，该化合物是Macrocentrus grandii的性信息素。，而在二肽抗菌素的合成中，使用2-甲基苯并咪唑的异构化反应被用于γ-内酯中间体的高度立体选择性合成。这些庞大的质子源将是实现天然产物的简明合成的有力工具。