Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Intramolecular addition of heterofunctionalities to C=C double bonds without P-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl3 center dot nH(2)O (10 mol%) and 3 equiv. of AgOTf acted as a catalyst for cyclization of 2-allylphenol (la) 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*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 To1BINAP as a ligand, over 60% e.e. was achieved. (c) 2006 Elsevier B.V. All rights reserved.