The reductive coupling of phthalimides with ketones and aldehydes by Zn-TiCl4 in THF gave two- and four-electron reduced products, 3-hydroxy-3-(1-hydroxyalkyl)isoindolin-1-ones and alkylideneisoindolin-1-ones, selectively by controlling the reaction conditions. Therefore, the one-pot synthesis of alkylideneisoindolin-1-ones from phthalimides was effected by this reaction. Although the alkylideneisoindolin-1-ones prepared from phthalimides and aldehydes were formed as mixtures of geometric isomers in most cases, the geometric ratios could be increased by reflux in cat. PPTS/toluene. After the isomerization, the E-isomers of N-methyl substituted alkylideneisoindolin-1-ones (X = Me, R(1) = R, R(2) = H) and the Z-isomers of N-unsubstituted alkylideneisoindolin-1-ones (X = H, R(1) = H, R(2) = R) were obtained preferentially.
Synthesis of Alkylideneisoindolin-1-ones. -The title reaction promoted by Zn-TiCl 4 gives two-and four-electron reduced products, (hydroxyalkyl)isoindolinones and alkylideneisoindolinones, selectively in dependance on the reaction conditions used. Alkylideneisoindolinones prepared from phthalimides and aldehydes are obtained as mixtures of geometric isomers. In most cases, the geometric ratios can be increased by treatment with catalytic amounts of pyridinium tosylate. After isomerization, the E-isomers of N-methyl substituted alkylideneisoindolinones and the Z-isomers of N-unsubstituted alkylideneisoindolinones are obtained preferentially [shown only for (VIIIe)]. -(KISE*, N.; KAWANO, Y.; SAKURAI, T.; J. Org. Chem. 78 (2013) 24, 12453-12459, http://dx.
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