Exploiting Chalcogen-Containing Compounds in Donor-Acceptor Cyclopropane and Cyclobutane Chemistry: Access to Four- to Nine-Membered Heterocycles

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In this project, reactions of donor-acceptor cyclopropanes and cyclobutanes with chalcogen-containing compounds will be investigated. Previous work by the group has shown that their high nucleophilicity is ideally suited to initiate ring opening and cycloaddition reactions of these polarized three-membered rings.In the first sub-project, donor-acceptor cyclopropanes are to be expanded into the corresponding four-membered rings under Lewis acid catalysis by inserting a chalcogen atom (S or Se). Reagents that not only contain a nucleophilic chalcogen but also carry a corresponding leaving group on the chalcogen (e.g. thiosulfonates, RSeSeLi etc.) are to serve as chalcogen carriers. A slightly modified reaction design should also allow the insertion of two chalcogens, be they the same or different, into the corresponding five-membered rings with endo-dichalcogenide subunits. Similar reactions should be carried out on the slightly less strained donor-acceptor cyclobutanes in order to arrive at analogous five- and six-membered rings containing chalcogens. With the aid of chiral ligands that complex the Lewis acid, some of these transformations should also be carried out with a dynamic kinetic resolution.The second subproject is devoted to (3+4) -, (3+5) - and (3+6)-cycloadditions of donor-acceptor cyclopropanes with four, five and six atomic components to build seven-, eight- and nine-membered ring systems. In order to obtain sulfur-containing seven-membered rings, benzothietes as a 4-atom component are to be reacted with the polarized three-membered rings under Lewis acid catalysis. The synthesis of eight-membered rings based on the cyclopropanes is to be carried out by means of synergistic catalysis. Vinyl-substituted epoxides, thiiranes and also aziridines as 5-atom components are to be activated by means of Pd catalysis and reacted with the three-membered rings activated by a Lewis acid. Similar reactions starting from vinyl-substituted oxetanes, thietanes and azetidines as 6 atom components should allow access to nine-membered ring systems. The enantioselectivity of the reactions could be controlled by means of chiral ligands on the Lewis acid as well as on the Pd to give a matched or mismatched case.