Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes

• Grzegorz Mlostoń,
• Mateusz Kowalczyk,
• André U. Augustin,
• Peter G. Jones and
• Daniel B. Werz

Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109

• -arylcyclopropane dicarboxylates reacted with the corresponding aryl ferrocenyl thioketones in a completely diastereoselective manner to form single products in which (C-2)-Ar and (C-5)-ferrocenyl groups were oriented in a cis-fashion. In contrast, the same cyclopropanes underwent reaction with alkyl ferrocenyl

• thioketones to form nearly equal amounts of both diastereoisomeric tetrahydrothiophenes. A low selectivity was also observed in the reaction of a 2-phthalimide-derived cyclopropane with ferrocenyl phenyl thioketone. Keywords: [3 + 2]-cycloaddition reactions; donor–acceptor cyclopropanes; ferrocenyl

• , in further experiments of ferrocenyl thioketones 8 with differently substituted cyclopropanes 5. Again using Sc(OTf)3, we repeated the experiment with 8a, which this time led to the isolation of 9a in an excellent yield of 98% (Table 1). In analogy to 8a, the similarly substituted ferrocenyl (β

Synthesis of ferrocenyl-substituted 1,3-dithiolanes via [3 + 2]-cycloadditions of ferrocenyl hetaryl thioketones with thiocarbonyl S-methanides

• Grzegorz Mlostoń,
• Róża Hamera-Fałdyga,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 1421–1427, doi:10.3762/bjoc.12.136

• with aromatic and heteroaromatic thioketones [7][9]. Furthermore, the analogous reaction mechanism was postulated to explain the results obtained with thiocarbonyl S-ethanides, S-isopropanides, and S-(trimethylsilyl)methanides [10]. Ferrocenyl thioketones have never been exploited in reactions with

• thiocarbonyl S-methanides with aryl and hetaryl thioketones, we propose that the reactions with ferrocenyl thioketones 1 occur predominantly via an intermediate 1,5-diradical. The formation of the sterically more crowded 1,3-dithiolanes 5a–g confirms that the stabilized 1,5-diradicals of type 7 (Scheme 4) are

• results in the preferred concerted [3 + 2]-cycloaddition. It is well known that this mechanism, controlled by frontier-orbital (FMO) interactions, is strongly influenced by steric effects in the case of C=S dipolarophiles [8][17]. Conclusion The presented study indicated that ferrocenyl thioketones show