Synthesis of α-Ketobutyrolactones and γ-Hydroxy-α-Keto Acids.

In connection with the studies for developing new enzymes that could be useful in organic synthesis, practical preparation of racemic and enantiopure forms of γ-hydroxy-α -keto acids has been successfully achieved. For racemic form of γ-hydroxy-α -keto acids, indium-mediated allylation of aldehydes with 2-(bromomethyl)acrylic acid has been employed as a key step. Oxidative cleavage of the thus formed 2-methylenebutyrolactones provided the desired α -ketobutyrolactones. Enzymatic resolution of the γ-hydroxy-α -methylene esters provided the desired γ-hydroxy-α -methylene acids which were successfully converted to γ-hydroxy-α -ketobutyrolactones in optically pure forms.