An efficient route to a variety of 2-phenylindolin-3-ones from amino acid methyl esters has been developed. The reaction of amino acid methyl esters with benzyne prepared from 2-(trimethylsilyl)phenyl triflate and CsF gave 2-phenylindolin-3-ones in moderate to good yields.
Aldolization reactions of 1-acetyl-1H-indol-3(2H)-one with glyoxal derivatives afforded (1-acetyl-3-oxo-2,3-dihydro-1H-indol-2-ylidene)acetic acid ester derivatives 2 and 3. Spiro compounds 6 were obtained by Diels-Alder reactions of 2; inverse electron demand Diels-Alder reactions of 2 afforded pyrano indoles 8.