allo-Threonine-derived oxazaborolidinone (OXB) catalyzes the Friedel-Craftsalkylation of furans and indoles with simple acyclic α,β-unsaturated ketones to give the products in high yields and with high enantioselectivities. With 5-10 mol% of the OXB catalyst, enantioselectivities of up to 94% ee could be achieved for a variety of substrates. The use of N,N-dimethylaniline (2.5-10 mol%) as an additive
Asymmetric Mukaiyama Aldol Reaction of Nonactivated Ketones Catalyzed by <i>allo</i>-Threonine-Derived Oxazaborolidinone
作者:Shinya Adachi、Toshiro Harada
DOI:10.1021/ol802087u
日期:2008.11.6
Asymmetric Mukaiyama aldol reaction of nonactivated ketones is realized for the first time by using an oxazaborolidinone catalyst derived from O-benzoyl-N-tosyl-allo-threonine. By employing a dimethylsilyl ketene S,O-acetal as a nucleophile, a variety of acetophenone derivatives afford the corresponding tertiary beta-hydroxy carbonyl compounds with high enantioselectivity up to 98% ee.
Asymmetric Mukaiyama−Michael Addition of Acyclic Enones Catalyzed by <i>a</i><i>llo</i>-Threonine-Derived <i>B</i>-Aryloxazaborolidinones
[GRAPHICS]O-(2-Naphthoyl)-N-tosyl-L-allo-threonine B-phenyloxazaborolidinone catalyzes the asymmetric Mukaiyama-Michael addition of simple acyclic enones to give adducts of 54-85% ee, 2,6-Diisopropylphenal as an additive is demonstrated to effectively retard the undesirable Si+-catalyzed racemic pathway.
Oxazaborolidinone-Catalyzed Enantioselective Diels−Alder Reaction of Acyclic α,β-Unsaturated Ketones
[GRAPHICS]allo-Threonine-derived O-acyl-B-phenyl-oxazaborolidinones are demonstrated to be powerful and highly enantioselective Lewis acid catalysts for the Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % of catalyst, the Diels-Alder adducts are obtained in 76-98% ee with high endo-selectivity. The catalyst exhibits high activity for the reaction with the less reactive beta-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The application of the catalysts to the Diels-Alder reaction of furan is also described.
Oxazaborolidinone-Catalyzed Enantioselective Friedel−Crafts Alkylation of Furans and Indoles with α,β-Unsaturated Ketones
allo-Threonine-derived oxazaborolidinone (10 mol %) catalyzes the Friedel−Craftsalkylation of furans and indoles with simple acyclic α,β-unsaturated ketones to give products with high yield and high enantioselectivity. The use of N,N-dimethylaniline (2.5−10 mol %) as an additive is essential for enantioselectivity.