An efficient one-pot synthesis of spiro dihydrofuran oxindole and spiro 2-hydroxytetrahydrofuran oxindole derivatives via (3+2) oxidative cycloaddition mediated by CAN
Spiro dihydrofuran oxindole derivatives were prepared via a (3+2) oxidative cycloaddition of 1,3-dicarbonyl compounds to 3-(phenyl-2-oxoethylidene)-1-methyloxindole and 3-benzylidene-1-methyloxindole derivatives mediated by ceric ammonium nitrate. In the case of the reaction of 3-(phenyl-2-oxoethylidene)-1-methyloxindole derivatives with acyclic 1,3-dicarbonyl compounds, spiro 2-hydroxytetrahydrofuran
(E)-2-Oxoindolin-3-ylidene ketones can be easily isomerized to their (Z)-isomers by AlCl3 at room temperature in CH2Cl2. The behaviour of the unsaturated dicarbonyl framework in the (Z)-configuration as a bidentate ligand can be the key-step of the isomerization. The limits of a reaction that allows to prepare several yet-unknown products is discussed.