The chiral, nucleophilic catalyst TADMAP (1) has been prepared from 3-lithio-4-dimethylaminopyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient, and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity.
Cyclooctatetraenes (COTs) are a fascinating class of molecules with great potential utility as building blocks for synthesis, [1] scaffolds for drug discovery, designed carbohydrate mimics, [2] ligands for d-and f-block metals [3] including those for asymmetric catalysis, [4] and components for molecular detection devices (e.g. dynamic molecular tweezers) [5] and novel materials.[6] For many applications including the use of COTs in fluxional materials, [7] conducting polymers, [8] and light emitting devices, [9] the type and degree of COT substitution play a critical role in controlling the redox and electronic properties of the system. For other applications, substitution determines COT topological chirality and the rate of COT racemization by tub-to-tub ring inversion.
The first [4+2+2] cycloadditions involving terminal alkynes and diene-enes, including a fully intramolecular example, are reported resulting in the formation of cyclooctadienes using [RhCl(CO)2]2 (5 mol %) treated with AgSbF6 (10 mol %) as a precatalyst. The reaction is general for a variety of terminal alkynes, as well as variously substituted diene-enes (yields up to 88%).
Eine Ni0‐katalysierte [2+2+2+2]‐Cycloaddition von 1,6‐Diinen liefert hoch funktionalisierte sechs‐ und achtfach substituierte Cyclooctatetraene (COTs) (siehe Bild), darunter das erste Beispiel für das Produkt einer vollständig intramolekularen [2+2+2+2]‐Cycloaddition. Die Regioselektivität dieses Prozesses wird untersucht, und die erste Verwendung eines COT‐Liganden wird am Beispiel eines Bisoxazolin‐COT‐Komplexes von ZnII aufgezeigt (rechts).
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