|Budget Amount *help
¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 2000 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1999 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1998 : ¥2,100,000 (Direct Cost : ¥2,100,000)
We have devised a new asymmetric boron-mediated asymmetric double aldol reaction. Treatment of a chiral acetate ester with dicyclohexylboron triflate and triethylamine, followed by the reaction with aldehyde, afforded bis-aldols via a double aldol reaction with high selectivity. Chiral triols of C3-symmetry, which are potential precursors for the study of asymmetric catalysis and chiral recognition, have been synthesized from the double aldol products. Preliminary studies on the derivatization of the triols as well as the preparation of their metal complexes have been executed.
From the mechanistic study, the characteristic features of this novel reaction can be summarized as follows : (1) the double aldol reaction is specific to acetate esters, not to ketones or thioesters, (2) the stoichiometry of the boron triflate to acetate ester is 2 : 1 to achieve enolization of the acetate ester, (3) the second equivalent of the boron triflate is active for the double aldol reaction but inactive for enolization of an external thioester, (4) a β-boryloxyester, which is an intermediate of the single (conventional) aldol reaction, is not an intermediate of the double aldol reaction. We have clarified the mechanism of the double aldol reaction, and spectroscopically characterized an intermediate enolate species as a "doubly borylated enolate", which is the first carbon-bound boron enolate species.