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Gold Catalysis: Catalyst Oxidation State Dependent Dichotomy in the Cyclization of Furan-Yne Systems with Aromatic Tethers
Ist Teil von
Chemistry : a European journal, 2013-01, Vol.19 (1), p.382-389
Ort / Verlag
Weinheim: WILEY-VCH Verlag
Erscheinungsjahr
2013
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Four different synthetic strategies led to a variety of furan–yne systems that contained an aryl system in the tether. Due to the short routes to these systems (four steps or less), a small library of substrates could easily be prepared. These were treated with AuCl3 or with the Gagosz’s catalyst Ph3PAuNTf2 complex. The AuCl3‐catalyzed reactions delivered highly substituted fluorene derivatives, a class of compounds of great importance as precursors for luminophores with extraordinary abilities. Conversely, a different mechanistic pathway was observed with the cationic gold(I) catalyst. In the latter case, a mechanistically interesting reaction cascade initiated a formal alkyne insertion into the furyl‐sp3‐C bond, which gave indene derivatives as the final products. This new reaction pathway depends on the aromatic moiety in the tether, which stabilizes a crucial cationic intermediate as a benzylic cation.
Flick the switch: Depending on the oxidation state of the gold catalyst, a reaction pathway involving either a gold‐catalyzed phenol synthesis or an insertion of the alkyne into the furyl‐sp3‐C bond is induced (see scheme).