Synthesis of Chiral Phthalimidine Derivatives

Phthalimidines (isoindolin-l-ones) can be valuable intermediates for the synthesis of isoindoles and some natural products, and there has been recent interest in the development of simple methods for the direct conversion of o-phthalaldehyde into /V-substituted phthalimidines. Condensation of o-phthalaldehyde with primary aliphatic amines using acetonitrile as solvent gives disappointing yields with a-methylbenzylamine, for example, the yield of the phthalimidine 1 is only 21%. By contrast, treatment of o-phthalaldehyde with a-amino acids in hot acetonitrile gives generally excellent yields of the corresponding phthalimidines. With L-valine, for example, 2 is formed in 87% yield. 

Suggest mechanisms for the formation of 1 and 2 which account for the higher yields observed when a-amino acids are used rather than the primary amines. 

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