A new immobilization scheme for enantioselective catalysts was developed by using a combination of ionic liquids and compressed CO2. Under continuous flow conditions, stable conversion and asymmetric induction was achieved over more than 60 h in the enantioselective Ni‐catalyzed hydrovinylation of styrene. While the ionic liquid dissolves and activates the organometallic catalyst in a tuneable manner, the presence of compressed CO2 greatly facilitates mass transfer and gives easy access to continuous processes (see the schematic representation).

Aromatic acylamido carbonyl compounds are readily cyclized to indole derivatives upon treatment with low-valent titanium reagents of the formal oxidation states 0, +1, and +2. Other strong reducing agents such as Sml2 and low-valent zirconium, niobium, and tungsten complexes are also capable of effecting such intramolecular alkylidenation reactions of amides. From the preparative point of view these heterocycle syntheses are best effected with an active titanium species which is prepared in the presence of the carbonyl compound upon coordination of TiCl" (re = 3, 4) to the oxo amide substrate and reduction of this complex with zinc dust ("instant" method). This procedure turned out to be as effective as the titanium-graphite-based methodology previously described but is much easier to perform as all hazardous reagents are avoided. "Instant" cyclizations can also be run in nonethereal solvents such as DMF, ethyl acetate, or acetonitrile and turned out to be compatible with many functional groups. The method was used to cyclize oxo amide 15 to (+)aristoteline, and it applies nicely to the synthesis of strained indole derivatives, the formation of benzo[6]furans, conventional McMurry reactions of aldehydes and ketones, and the dimerization of alkynes. Metals such as zirconium can also be activated in situ by reduction of ZrCl4 in the presence of a carbonyl compound. On the basis of the results obtained with substrates bearing appropriate structural probes a mechanism for such intramolecular keto-amide coupling processes is proposed. Carbonyl dianions, formed upon two-electron reduction of the keto group, are the most likely reactive intermediates. Electrochemical investigations support this mechanistic interpretation.

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Eine neue Immobilisierungsmethode für enantioselektive Katalysatoren wurde entwickelt, die auf der kombinierten Verwendung von ionischen Flüssigkeiten und komprimiertem CO2 beruht. Unter Durchflussbedingungen wurde bei der enantioselektiven Ni‐katalysierten Hydrovinylierung von Styrol über mehr als 60 h stabiler Umsatz und asymmetrische Induktion erreicht. Die ionische Flüssigkeit löst den metallorganischen Komplex unter Aktivierung und steuert seine katalytischen Eigenschaften, während das komprimierte CO2 den Massentransfer erleichtert und die kontinuierliche Prozessführung ermöglicht (siehe schematische Darstellung).

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