Platinum enolates addition reactions

Pt(II). Fujimura has developed a Pt(II)-catalyzed process for the addition of iso-butyrate-derived silyl ketene acetal 97 to aldehydes (Eq. (8.27)) [43]. The process utilizes a readily available Pt(Il) complex (98) that is generated in situ and can be easily handled in the laboratory [44]. In the presence of 5 mol% each of 98, triflic acid, and lutidine, 97 undergoes addition to aldehydes to afford a mixture of tri-methylsilyl-protected 99 and free alcohol 100 products in up to 95% ee. A thorough examination of the reaction conditions and their effect on the product selec-tivities has revealed that the addition of water and oxygen to the catalyst mixture leads to significant improvement in the optical purity of the products. A number of spectroscopic studies by P NMR and IR has led Fujimura to postulate that the reaction involves a carbon-bound platinum enolate intermediate in the catalytic cycle. 

Only in exceptional cases is it possible to isolate the enol ether, as with the addition of methanol to acetylenedicarboxylic esters [43], in good yields (eq. (19)). Catalysts which have been used in this reaction are palladium chlorides and platinum chlorides with bidentate phosphine ligands. 

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