Thermal reactions of the CF3
2+ dication with argon lead to the formation of an ArCF2
2+ dication, a new type of metastable species with an argon−carbon bond. None of the other rare gases undergo a similar reaction with CF3
2+. For the lighter rare gases (He and Ne), no reactions with CF3
2+ other than those due to electronically excited reactant ions are observed, whereas for the heavier rare gases (Kr and Xe), the prevailing reactive pathways involve single-electron transfer. At elevated collision energies, single-electron transfer predominates for collisions with all rare gases (He−Xe).
Irradiation with Er:YAG laser radiation before debonding of ceramic brackets significantly decreases the bonding failure and amount of remaining adhesive.
Two different enantioselective organocatalytic cascade reactions to form new sulfur‐containing spirocyclic scaffolds are described. In the first approach, benzothiophen‐2‐one and enals react in the presence of a secondary amine catalyst through a Michael/Michael/Aldol sequence to afford the final spiro‐cyclohexene carbaldehydes in good yields (up to 68 %) and with excellent selectivities [20:1 diastereomeric ratio (dr), up to 99 % ee]. In the second approach, the double Michael addition of benzothiophen‐2‐one to aromatic dienones with primary amine catalysis produces the corresponding spiro‐cyclohexanones in good yields (up to 76 %) and with moderate‐to‐high selectivities (up to 12:1 dr, up to 90 % ee). Moreover, the use of N‐phenylrhodanine as the bis‐nucleophile for these reactions also allowed the formation of the corresponding spirocyclic adducts.
Pyrazolones [1] are common heterocycles that are present in several pharmacologically active compounds, such as Metamizole (Scheme 1), a powerful analgesic and antipyretic developed by Hoechst AG in 1920. More recently, pyrazol-3-ones were found to be inhibitors of the cluster of differentiation 80 (CD80) protein, and to have potent activity in inhibiting protease-resistant prion protein accumulation, cytokines, and p38 kinases. Pyrazol-3-ones have also been studied as multidrug resistance modulators. [2] Despite the interest in pyrazolones as common structural motifs in pharmacologically active compounds, there are few methods that allow the construction of pyrazolones in asymmetric form. For example, Yuan and co-workers described a highly enantioselective pyrazolone addition to nitrostyrenes catalyzed by thiourea compounds, which gives the resulting chiral pyrazolones in high enantio and diaste-[a] M. Š imek, M. Remeš, Dr. J. Veselý Scheme 1. Biologically active pyrazolones.Scheme 2. Previous organocatalytic methods for pyrazol-3-one developed in our group. TMS = trimethylsilyl.
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