We report a new and readily accessible class of titanium salalen complexes derived from cis‐1,2‐diaminocyclohexane (cis‐DACH) and fluorinated salicylic aldehyde derivatives. With aqueous hydrogen peroxide as the oxidant, these complexes catalyze the epoxidation of terminal, nonconjugated olefins in high yields with high enantioselectivities. We furthermore discovered that the addition of certain acidic or basic co‐catalysts significantly accelerated the epoxidation. For example, in the presence of 1 mol % Ti catalyst and 1 mol % pentafluorobenzoic acid, 1‐octene epoxidation (95 % ee) was completed at room temperature within 8 h. The catalytic process was compatible with many functional groups (e.g., ethers, esters, halides, nitriles, and nitro groups), whereas free hydroxy groups appeared to slow down the reaction to some extent. Catalyst recycling was possible.
A titanium(III)-catalyzed radical cyclization to unprotected 3-aminoindoles, 3-aminopyrroles, or 3-iminoindolines is reported. The reaction is non-hazardous, scalable, and allows facile isolation of the free products by extraction. The method is demonstrated on a large substrate scope and it further allows the direct installation of various nitrogen protecting groups or the synthesis of building blocks for peptide chemistry in a single sequence. Fused bisindoles can be directly accessed from the cyclization products.
The exceptionally mild conditions of at itanium(III)-catalyzed cyclization reactionp aired with ac onvenient acid/base extraction have enabled the straightforward synthesis, isolation, and direct N-functionalization of amino heterocycles such as 3-aminoindoles and -pyrroles.T he unprotected heterocycles are ideal building blocks fort he installation of aminatedi ndoles and pyrroles into target molecules, but their sensitivity has previously impeded their synthesis by modernc atalytic methods. This full paper presents the development and extended scope of the new cyclization methodology.T he transformation of the products into fused bis-indoles is also demonstrated along with the discoveryo f an unusual palladium-catalyzed reductive biphenyl coupling reaction. The titanium(III)-catalyzed cyclization hasa lso been appliedt ot he synthesis of substituted 3-iminoindolines, which are of potential interestf or applicationsi nn atural product synthesis and exhibit tunable blue-to-green fluorescence properties.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.org/10.1002/chem.201805909.Scheme1.a) Usualand ideal scenarios for the catalytic synthesis of 3-aminoindole and -pyrrole building blocks. b) Envisionedtitanium(III)-catalyzed cyclization to furnish unprotected, electron-rich 3-aminoheterocycles.
Es wird eine Titan(III)-katalysierte Radikalcyclisierung zu ungeschützten 3-Aminoindolen, 3-Aminopyrrolen oder 3-Iminoindolinen vorgestellt. Die Reaktion ist ungefährlich,skalierbar und ermçglicht die leichte Isolierung der freien Produkte mittels Extraktion. Die Methode zeigt eine große Substratbandbreite auf und ermçglicht die direkte Stickstoffschützung oder Synthese von Peptidbausteinen in einer einzelnen Sequenz. Anellierte Bisindole sind ebenfalls aus den Cyclisierungsprodukten zugänglich.
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