Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Intramolecular addition of heterofunctionalities to CC double bonds without β-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl3 · nH2O (10 mol%) and 3 equiv. of AgOTf acted as a catalyst for cyclization of 2-allylphenol (1a) to 2,3-dihydro-2-methylbenzofuran (2a) in good yield in the presence of Cu(OTf)2 as a co-catalyst and PPh3 as a ligand. This catalyst system also catalyzed the cyclization of 2-allylbenzoic acid to lactone in 91% yield. Then, a new catalyst system (RuCp∗Cl2)2 (1.0 mol%)/4AgOTf/4PPh3, was found to be more active even in the absence of Cu(OTf)2. Furthermore, this catalysis was applied to asymmetric reaction of 2-allylphenol (1a). When using TolBINAP as a ligand, over 60% e.e. was achieved.

Intramolecular cyclization of 2-allylphenol (1a) to 2,3-dihydro-2-methylbenzofuran (2a) using ruthenium catalyst in good yield with moderate enantioselectivity.Figure optionsDownload as PowerPoint slide