Activation of Quinolines by Cationic Chalcogen Bond Donors

Abstract

The application of already established as well as novel selenium- and sulfur-based cationic chalcogen bond donors in the catalytic activation of quinoline derivatives is presented. In the presence of selected catalysts, rate accelerations of up to 2300 compared to virtually inactive reference compounds are observed. The catalyst loading can be reduced to 1 mol% while still achieving nearly full conversion for electron-poor and electron-rich quinolines. Contrary to expectations, preorganized catalysts were less active than the more flexible variants.

Chalcogen Bonding Catalysis of a Nitro‐Michael Reaction

“…With tellurium‐based catalyst 7 , compound 3 was obtained in 78 % yield after 48 h (Table , entry 3) whereas the sulfur‐ and selenium‐based catalysts 7 and 7 were virtually inactive (Table , entries 1 and 2). Even though sulfur and selenium derivatives have been successfully used as ChB catalysts before, the order of activity observed here is surely well in line with ChB theory (see above). To confirm the aspired bidentate mode of activation of 7 , its mono‐chalcogenated analogue 9 was subsequently also investigated.…”

“…The coordination of ChB donors to neutral compounds is surely weaker in strength, and so their activation is more challenging (even though the transition state may of course still be charged). Indeed, this concept has hitherto been limited to a handful of examples in which ChB donors enable the reduction of quinolines, and to a very recent report on the activation of carbonyl compounds . In particular, the activation of nitro compounds has not been reported thus far for XB or ChB organocatalysis.…”

Carbonyl Activation by Selenium‐ and Tellurium‐Based Chalcogen Bonding in a Michael Addition Reaction

“…[9] In 2017, first such cases employing neutral sulphur-based or cationic selenium-basedc atalysts were reported by Matile [10] and our group, [5a] with the reactions involving the reductiono f quinolines anda nS N 1-based carbon-carbon bond formation, and similaro nes were being investigated later on. [5b, 11] Recently,o ur group could confirmt he superior performance of cationic chalcogen bondingc atalysts versusn eutralo nes in a direct comparison, [12] and we also reported the first activation of an itro group, [5c] using tellurium-based dicationic catalysts. Also in 2019, Wang et al described the use of bidentate selenophosphonium compoundsa sc atalysts in am ulticomponent reactioni nvolving several carbonyl species, which likely constitutes the first activation of this functional group by chalcogen bonding.…”

Noncovalent Chalcogen‐Bonding Catalysis Using ppm‐Level Catalyst Loading to Achieve Cyanosilylation of Ketones

“…[7] In contrast, the exploration of intermolecular chalcogen-bonding interaction in solution remains underexplored, and there are only a handful of examples on anion recognition, [8] transport, [9] and catalysis. [10][11][12][13][14][15] While chalcogen-bonding catalysis would provide a promisingly new tool to drive chemical reactions, however, the research toward this direction has met with very limited progress. Chalcogen-bonding catalysis was only demonstrated to be feasible in few reactions, i. e. the reduction of quinoline with Hantzsch ester, [11] the abstraction of halide in the S N 1-type reactions [12] and the activation of carbonyl group in the assembly reactions and the Michael addition reactions, [13] by Matile, Huber and our group.…”

“…Very recently, tellurium-based chalcogen-bonding activation was achieved in the Michael addition reactions [14] and the reduction of quinoline with Hantzsch ester activated by a chalcogen bond was revisited. [15] We also developed a dual chalcogen-chalcogen bonding catalysis strategy which was demonstrated by the achievement of the Rauhut-Currier-type reactions. [16] While these achievements show the feasibility of chalcogen-bonding catalysis and have significantly advanced this concept, however, in contrast to the other catalysis disciplines, the efficiency of chalcogenbonding catalysis remains the true challenge for the further development of this activation mode.…”