|Budget Amount *help
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,400,000 (Direct Cost: ¥2,400,000)
Recently, great success has been achieved in chiral Lewis acid catalyzed enantioselective reactions. Especially, those based on the activation of a carbonyl group, such as Diels-Alder reaction, aldol reaction, allylation reaction, and carbonyl-enereaction, have been developed extensively. One might think that these enantioselective reactions have been almost fully established. However, the substrates of the chiral Lewis-acid catalyzed reactions are usually aldehydes and bidentate carbonyl compounds. It is most recently that the chiral Lewis acid catalyzed enantioselective reactions of ketones have become an area of intense research activity. In the present research work, we developed a new oxazaborolidinone (OXB) catalysts derived from allo-threonine for the asymmetric Diels-Alder reactions of acyclic α,β-unsaturated ketones. The application of the OXB catalysts to the asymmetric aldol reaction of ketones was also examined.
Asymmetric Diels-Alder Reaction of Unsaturated Ketones : O-p-Biphenoyl OXB was demonstrated to be a powerful and highly enantioselective Lewis-acid catalyst for enantioselective Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % the catalyst, the Diels-Alder adducts are obtained up to 94 % ee with high endo-selectivity. The catalyst exhibited high activity for the reaction with the less reactive B-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The OXB catalyst also showed high selectivity in the reaction of furan and vinyl ketones especially when less polar solvent was used.
Asymmetric Aldol Reaction of Ketones: In the presence of O-benzoyl OXB catalyst (20 mol%), the reaction of acetophenone with a dimethylsilyl ketene S, O-acetal gave the corresponding aldol adduct of ca. 90% ee. Works are in progress to optimize reaction conditions and catalyst structures as well as to clarify the scope of substrates.