Highly selective metal mediated ortho-alkylation of phenol. First platinum containing organometallic chromane analogues

We were able, for the first time, to synthesize and characterize Pt derivatives with a structural shape similar to vitamin E, having a metalla-chromane core. The formation reaction mechanism includes an unexpected highly selective ortho aromatic electrophilic substitution on phenol, operated by [PtCl(eta(1)-C2H4OR)(N-N)], R = Me or Ph, and a final cyclization step. The X-ray structure of one of the new metalla-chromane complexes [Pt(EtPh)(phen)], 1a, (EtPh = 2-(ethan-2'-yl-kC(1))-1-phenolato-kO(1), phen = 1,10- phenanthroline) is reported. Cytotoxicity and Pt uptake measurements, performed on HeLa cancer cells, show an interesting structure-activity correlation for the new metalla-chromane analogues 1a and [Pt(MeOEtPh)(phen)], 1b, (MeOEtPh = 2-( ethan-2'-yl-kC(1))-4-(methoxy)-1-phenolato- kO(1)), being the structurally closest to vitamin E and also the most active.