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1.
J Org Chem ; 68(26): 10046-57, 2003 Dec 26.
Article in English | MEDLINE | ID: mdl-14682699

ABSTRACT

allo-Threonine-derived O-aroyl-B-phenyl-N-tosyl-1,3,2-oxazaborolidin-5-ones 1g,n catalyze the asymmetric Mukaiyama-Michael reaction of acyclic enones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions. The effects of the additives are discussed in terms of the retardation of an Si(+)-catalyzed racemic pathway, which seriously deteriorates the enantioselectivity of asymmetric Mukaiyama-Michael reactions. A working model for asymmetric induction is proposed based on correlation between catalyst structures and enantioselectivities.

2.
Chirality ; 15(1): 28-30, 2003 Jan.
Article in English | MEDLINE | ID: mdl-12467039

ABSTRACT

In the presence of 2,6-diisopropylphenol and t-BuOMe (1 equiv. each), asymmetric Mukaiyama-Michael reaction of a variety of benzalacetone derivatives 2 with silyl ketene acetal 3 is efficiently catalyzed by O-(2-naphthoyl)-N-tosyl-(L)-allo-threonine-derived B-phenyloxazaborolidinone 1 (10 mol%) to give the corresponding adducts 5 in 60-90% ee.


Subject(s)
Acetone/analogs & derivatives , Acetone/chemistry , Benzene Derivatives/chemistry , Oxazoles/chemistry , Threonine , Molecular Conformation , Molecular Structure , Oxazoles/chemical synthesis , Stereoisomerism
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