Directing groups have been widely used in recent years to achieve control over all aspects of reaction selectivity in a wide range of transformations involving transition-metal catalysis and organometallic reagents. In cases when the existing functional group within a substrate is unsuited to achieve efficient intramolecular delivery of a reagent or catalyst, the specific introduction of an appropriately designed removable reagent-directing group can be a solution to this problem. In this Review we give an overview of the state of the art in this area, including the stoichiometric and catalytic use of directing groups.
Dirigierende Gruppen haben in den vergangenen Jahren breite Anwendung gefunden, um Reaktionsselektivitäten in einem breiten Spektrum an übergangsmetallkatalysierten Reaktionen und Reaktionen metallorganischer Reagentien zu steuern. In Fällen, in denen die im Substrat vorhandenen funktionellen Gruppen nicht geeignet sind, um eine effiziente intramolekulare Reagens‐ oder Katalysator‐Steuerung zu ermöglichen, kann das gezielte Einbringen von maßgeschneiderten und wieder entfernbaren reagensdirigierenden Gruppen eine Lösung für dieses Problem bieten. In diesem Aufsatz geben wir eine Überblick zum Stand der Forschung auf diesem Gebiet und schließen dabei sowohl den stöchiometrischen wie den katalytischen Einsatz dirigierender Gruppen ein.
The preparation and functionalization of spirocyclohexa-2,5-diene oxindoles is described. The spirocyclic core of the title compounds was installed by using a SmI(2)-mediated cyclization of aryl iodobenzamides. Epoxidation with CF(3)CO(3)H was then carried out and was shown to occur with a high level of diastereocontrol: the reagent approaches the diene moiety syn to the amide group, which is likely to be as a consequence of hydrogen bonding between the amide C=O bond and the peracid hydrogen. Carbanionic functionalization of the spirocyclohexa-2,5-diene oxindoles was then examined, leading to an unprecedented rearrangement of the strained spiro system into dearomatized phenanthridinones. Upon treatment with lithium diisopropylamide (LDA) at -40 degrees C, the dienes rearranged to provide a phenanthridinone lithium enolate intermediate that was trapped by electrophiles including alkyl halides and aldehydes. Interestingly, alkylation and hydroxyalkylation occurred with different regiocontrol. DFT calculations were performed that rationalize the observed skeleton rearrangement, emphasizing the role of LDA/diisopropylamine in this rearrangement. The proposed mechanism thus relies on a thermodynamically driven diisopropylamine-mediated proton transfer with the cleavage of the diene-amide C=O bond as the key step.
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