Optisch aktive O-Silyl-β-dicarbonylverbindungen. IV. Transsilylierungsreaktionen

Optically Active O-Silyl-β-dicarbonyl Compounds. IV. Transsilylation Reactions The relationship between the structure of O-silyl-β-dicarbonyl compounds and their tendency to transsilylation reactions is studied by gas chromatography. It is shown that the silyl derivatives of β-diketones and β-dicarboxylic acid diesters easily undergo intermolecular mutual transsilylation reactions. The same compounds quickly transfer silyl groups to free β-dicarbonyl compounds. On the contrary, with silyl derivatives of β-keto esters, o-acylphenols and salicylic acid esters no transsilylation reaction could be observed, and the transfer of silyl groups from O-silyl-β-keto esters to free β-keto esters is only very slow. The ease of transsilylation reactions of O-silyl-β-dicarbonyl compounds correlates with the velocity of racemization of optically active O-silyl-β-dicarbonyl compounds of the same structure. Therefore, we assume that intermolecular transsilylation reactions with inversion of configuration are the main reason for the racemization of optically active O-silyl-β-dicarbonyl compounds. However, no connection could be found between the tendency to transsilylation reactions and the stereochemistry of the reactions of optically active O-silyl-β-dicarbonyl compounds with LiAlH₄ which is also dependent on the structure of these compounds.