Abstract
Cyclophanes are a venerable class of macrocyclic and/or cage compounds that often feature high strain, unusual conformations and quite surprising properties, many of which are legendary in physical organic chemistry. However, the discovery of new, diverse cyclophanes and derivatives has been hindered by syntheses that are traditionally low-yielding, requiring long reaction times, laborious purification steps and often extreme conditions. Herein, we demonstrate a new self-assembly route to a variety of discrete cyclic and caged disulfide structures, which can then be kinetically captured upon sulfur extrusion at room temperature to give a diversity of new thioether (hetera)cyclophanes in high yield. In addition to the synthesis of novel macrocycles (dimers through hexamers), this process provides an improved route to a known macrobicyclic trithiacyclophane. This technique also enables the facile isolation of a tetrahedral macrotricyclic tetrathiacyclophane in two steps at an ambient temperature.
Highlights
Cyclophanes are a venerable class of macrocyclic and/or cage compounds that often feature high strain, unusual conformations and quite surprising properties, many of which are legendary in physical organic chemistry
We have shown a selective, high yielding alternative to traditional cyclophane synthesis that uses self-assembly and capture through the use of a pnictogen additive to direct the self-assembly of discrete disulfidecyclophanes
Using a self-assembly approach eliminates the need for caustic, high-temperature methods and avoids low yields that result from the rapid formation of unfavourable insoluble oligomers. This method complements modern research on dynamic combinatorial covalent libraries of disulfides19,23 by providing a method to isolate and kinetically capture individual members of such equilibrating systems; in addition, the key pnictogen additive during the self-assembly step avoids the formation of disulfide polymers that plagued early efforts aimed at synthesizing discrete polydisulfides39,47
Summary
Cyclophanes are a venerable class of macrocyclic and/or cage compounds that often feature high strain, unusual conformations and quite surprising properties, many of which are legendary in physical organic chemistry. We demonstrate a new self-assembly route to a variety of discrete cyclic and caged disulfide structures, which can be kinetically captured upon sulfur extrusion at room temperature to give a diversity of new thioether (hetera)cyclophanes in high yield. The directing behaviour of the SbCl3 additive exhibits impressive resistance to insoluble disulfide polymer formation, long reactions times and low selectivity for a variety of different ligand systems. Using this self-assembly method, the isolation of previously unattainable disulfide cyclophanes—including trimers, tetramers, pentamers, hexamers and tetrahedra—is possible in a nearly instantaneous reaction from simple di- and tri-thiol ligands. We detail applications of our new method to the synthesis of a series of both known and entirely new cyclophanes
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