Oxidative Cyclization of -(1-Hydroxy-2-alkynyl)--tosylanilides for the Synthesis of 4-Quinolones.

The treatment of easily accessible -(1-hydroxy-2-alkynyl)--tosylanilides with excess manganese(IV) oxide in the presence of substoichiometric tetrabutylammonium iodide (TBAI) in chloroform (or in the absence of TBAI in dimethylformamide, DMF) promoted a sequential oxidation/intramolecular hydroamination to give 4-quinolones and/or ()-2-alkylidene-3-oxindoles ()- in good yields. Possibly, MnO played dual roles as an oxidant and as a Lewis acidic activator of intermediary ynones . The product distributions between and ()- could be controlled by the choice of solvents.