An effective method for the synthesis of 3,4-disubstituted quinolin-2(1H)-ones was reported. α-Carbonylalkyl radical, produced by the manganese(III) acetate oxidation of α-substituted N-[2-(phenylethynyl)phenyl]acetamides, undergoes a 6-exo-dig cyclization onto the C-C triple bond efficiently and 3,4-disubstituted quinolin-2(1H)-ones were produced. Heterocyclic substrates could also be used to generate the corresponding quinolin-2(1H)-ones smoothly. A variety of functional groups, including methoxycarbonyl, cyano, diethoxyphosphoryl and benzoyl groups, are compatible with the reaction conditions. Under Mn(II)/Co(II)/O2 conditions, the formation of these quinolin-2(1H)-ones could also be achieved from the corresponding N-[2-(phenylethynyl)phenyl]acetamides and a catalytic amount of manganese(II) acetate was used.
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