ArCH(OMe)₂--a Pt(IV)-catalyst originator for diverse annulation catalysis.

We discover an important property of a small molecule ArCH(OMe)₂ which transforms catalytically inactive Pt(II)Br₂ procatalyst in situ to an powerful catalyst Pt(IV)-species for diverse annulation reaction. The powerful catalytic system enables selective activation of C₂-H/N-H and C₂-H/C₄-H of acetoacetanilide and C=O/C≡C of substituted butyne-1,2-dione for C-C/C-N, C-C/C-C and C-O/C-O bond-forming inter- and intramolecular annulation towards direct syntheses of functionalised 2-pyridones, cyclohexenones and 3(2H)-furanones respectively. In contrast to the common ligand, herein highly labile C-OMe bond of ArCH(OMe)₂ is expected to react with PtBr₂ towards generation of the high-valent active catalyst. Unlike catalyst promoter or initiator, the reaction does not occur with PtBr₂ in the absence of ArCH(OMe)₂. In situ generation of Pt(IV)-species and -OMe fragment of ArCH(OMe)₂ were confirmed from the UV-vis characteristic peaks about 260 nm and trapping of -OMe group respectively. These observations provide new prospects and perspectives in catalysis for innovative catalyst design.