Cooperative chalcogen bonding interactions in confined sites activate aziridines

Abstract

The activation of aziridines typically involves the use of strong Lewis acids or transition metals, and methods relying on weak interactions are rare. Herein, we report that cooperative chalcogen bonding interactions in confined sites can activate sulfonyl-protected aziridines. Among the several possible distinct bonding modes, our experiments and computational studies suggest that an activation mode involving the cooperative Se···O and Se···N interactions is in operation. The catalytic reactions between weakly bonded supramolecular species and nonactivated alkenes are considered as unfavorable approaches. However, here we show that the activation of aziridines by cooperative Se···O and Se···N interactions enables the cycloaddition of weakly bonded aziridine-selenide complex with nonactivated alkenes in a catalytic manner. Thus, weak interactions can indeed enable these transformations and are an alternative to methods relying on strong Lewis acids.

(Pre)association as a crucial step for computational prediction and analysis of the catalytic activity of σ-hole donating organocatalysts

“…1, C–D ) compared to the uncharged catalysts A and B . 10,17–24 Moreover, the catalytic activity of the XB and ChB species featuring the halogen( iii ) or chalcogen( iv ) atoms ( E and F , respectively) is remarkably higher than that of halogen( i )- and chalcogen( ii )-containing species C and D , correspondingly. Thus, cationic iodine( i )-based catalysts C (in particular, iodoazolium salts 9,25–33 ) effectively catalyze a wide range of organic reactions, whereas cationic iodine( iii ) derivatives (iodonium salts E , X = I) featuring two σ-holes at the iodine atom possess even a higher catalytic activity.…”

Chalcogen Bonding Catalysis with Phosphonium Chalcogenide (PCH)

“…For instance, Se···Cl interactions were observed in the crystal structure of PCH4 (Figure C) . Furthermore, besides the presence of interactions between selenium and lone-pair (Se···LP) electron donors, chalcogen···π bonding is also feasible since intramolecular Se···π interactions were observed in the crystal structure of PCH7 (Figure D) …”

“…Several representative PCH catalysts are depicted in Scheme 1. [1][2][3][4]44 In a disubstituted chalcogenide, the electrons distributed around the chalcogen atom in an anisotropic way, thus possessing both positive and negative electrostatic regions. Specifically, the positive electrostatic region is highly directional, along the extension of the covalent bond of Ch−R, while the negative electrostatic region is located in the oblique direction.…”

“…These highly active PCH catalysts can be easily and modularly synthesized while there is plenty of room for structural modification from either the phosphonium part or the chalcogen part. Several representative PCH catalysts are depicted in Scheme . − , …”

“…Enabled by this cooperative Se···O and Se···N bond activation approach, a direct cyclization of aziridines 23 with nonactivated alkenes 24 was achieved to give pyrrolidines 25 in good yields (Scheme ), thus shifting stoichiometric Lewis acid mediated transformation to a weak interaction catalysis approach …”