In the last years the use of chalcogen bonding-the noncovalent interaction involving electrophilic chalcogen centers-in noncovalentorganocatalysis has received increasedi nterest, particularly regarding the use of intermolecularL ewisa cids. Herein, we present the first use of tellurium-based catalysts for the activation of ac arbonyl compound (and only the second such activation by chalcogen bondingi ng eneral). As benchmark reaction, the Michael-typea ddition between trans-crotonophenone and 1-methylindole (and its derivatives) was investigated in the presence of various catalyst candidates. Whereas non-chalcogen-bonding reference compounds werei nactive, strong rate accelerations of up to 1000c ould be achieved by bidentate triazolium-basedc halcogen bond donors, with product yields of > 90 %w ithin 2h of reaction time. Organotellurium derivatives were markedly more active than their seleniuma nd sulphur analogues and non-coordinatingc ounterions like BAr F 4 provide the strongest dicationic catalysts.Chalcogen bonding [1] denotes the attractive interaction between electrophilicc halcogen centers and Lewis bases.

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.

Recently, chalcogen bonding has been investigated in more detail in organocatalysis and the scope of activated functionalities continues to increase. Herein, the activation of imines in a Povarov [4+2] cycloaddition reaction with bidentate cationic chalcogen bond donors is presented. Tellurium‐based Lewis acids show superior properties compared to selenium‐based catalysts and inactive sulfur‐based analogues. The catalytic activity of the chalcogen bonding donors increases with weaker binding anions. Triflate, however, is not suitable due to its participation in the catalytic pathway. A solvent screening revealed a more efficient activation in less polar solvents and a pronounced effect of solvent (and catalyst) on endo : exo diastereomeric ratio. Finally, new chiral chalcogen bonding catalysts were applied but provided only racemic mixtures of the product.

Applications of both halogen and chalcogen bonding in organocatalysis are by now well established with various examples. However, the combination of both interactions within one catalyst is currently unknown. Herein, we describe the synthesis of such a mixed chalcogen‐ and halogen‐bond donor and present a first indication of its catalytic activity in a benchmark reaction.

Noncovalent interactions such as halogen bonding (XB) and chalcogen bonding (ChB) have gained increased interest over the last decade. Whereas XB-based organocatalysis has been studied in some detail by now, intermolecular ChB catalysis only emerged quite recently. Herein, bidentate cationic tellurium-based chalcogen bond donors are employed in the catalytic chloride abstraction of 1 chloroisochroman. While selenium-based ChB catalysts showed only minor activity in this given benchmark reaction, tellurium-based variants exhibited strong activity, with rate accelerations of up to 40 relative to non-chalogenated reference compounds. In general, the activity of the catalysts improved with weaker coordinating counterions, but tetrafluoroborate took part in a fluoride transfer side reaction. Catalyst stability was confirmed via a fluoro-tagged variant.