Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Abstract

Intramolecular addition of heterofunctionalities to C C double bonds without β-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl 3 · nH 2O (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 PPh 3 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 ∗Cl 2) 2 (1.0 mol%)/4AgOTf/4PPh 3, 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.