超强碱
化学
烷基化
氨基甲酸酯
羧化
催化作用
基质(水族馆)
烷基
离子液体
组合化学
有机化学
药物化学
海洋学
地质学
作者
Jere K. Mannisto,Ljiljana Pavlovic,Juha Heikkinen,Tony Tiainen,Aleksi Sahari,Norbert M. Maier,Kari Rissanen,Martin Nieger,Kathrin H. Hopmann,Timo Repo
标识
DOI:10.1021/acscatal.3c02362
摘要
We report a mild superbase-catalyzed and nitrogen-selective carboxylation of N-heteroaryls, with subsequent alkylation enabling the synthesis of drug-like O-alkyl carbamates in good yields (av. 86%). Our findings suggest a partial revision of the current mechanistic understanding as superbases upon mixing with indoles and azoles generally form uncharged hydrogen-bonded complexes and not ionic salts as previously proposed. However, when these complexes are exposed to CO2, carbamate salts are formed. These can be categorized into two subgroups, stable and fluxional carbamate salts, where the latter undergo fast and reversible CO2 exchange, thus being poor substrates for alkylation. Experiments and DFT calculations indicate that the fluxional behavior is primarily caused by substrate-specific electronic destabilization effects. The degree of destabilization depends on the number of nitrogen atoms within and the functional group substitution on the heterocyclic ring structures. Fluxionality can be compensated for by the use of lower temperatures and/or higher CO2 pressures as both measures stabilize the carbamate salts sufficiently, enabling subsequent alkylation.
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