Institut für Organische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104, Freiburg im Breisgau, Germany.
Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104, Freiburg im Breisgau, Germany.
Chemistry. 2019 Mar 1;25(13):3382-3390. doi: 10.1002/chem.201805909. Epub 2019 Feb 7.
The exceptionally mild conditions of a titanium(III)-catalyzed cyclization reaction paired with a convenient acid/base extraction have enabled the straightforward synthesis, isolation, and direct N-functionalization of amino heterocycles such as 3-aminoindoles and -pyrroles. The unprotected heterocycles are ideal building blocks for the installation of aminated indoles and pyrroles into target molecules, but their sensitivity has previously impeded their synthesis by modern catalytic methods. This full paper presents the development and extended scope of the new cyclization methodology. The transformation of the products into fused bis-indoles is also demonstrated along with the discovery of an unusual palladium-catalyzed reductive biphenyl coupling reaction. The titanium(III)-catalyzed cyclization has also been applied to the synthesis of substituted 3-iminoindolines, which are of potential interest for applications in natural product synthesis and exhibit tunable blue-to-green fluorescence properties.
钛(III)催化的环化反应条件异常温和，再加上方便的酸碱萃取，使得直接合成、分离和直接 N-官能化氨基杂环化合物（如 3-氨基吲哚和 -吡咯）成为可能。未保护的杂环化合物是将氨基吲哚和吡咯引入目标分子的理想构建块，但它们的敏感性以前阻碍了它们通过现代催化方法进行合成。本全文介绍了新的环化方法的发展和扩展范围。还展示了将产物转化为稠合双吲哚的方法，以及发现了一种不寻常的钯催化还原联苯偶联反应。钛(III)催化的环化也已应用于取代的 3-亚氨基吲哚啉的合成，它们在天然产物合成中有潜在的应用价值，并表现出可调谐的蓝绿光荧光性质。
