摘要:
A chiral cobalt(III) complex of a Schiff base derived from (R)-tryptophan and salicylaldehyde catalysed asymmetric trimethyl-silylcyanation of benzaldehyde at ambient temperature and a 20:1 substrate/catalyst ratio with the formation of enantiomerically enriched mandelonitrile (ee up to 77%).
摘要:
An efficient method for the asymmetric synthesis of C-aliphatic homoallylic amines with up to 94% yield and 80% de is reported. Ring-closing metathesis of several chiral homoallylic amines using the second-generation Grubbs catalyst provided easy access to a wide variety of cyclohexenylamines.
摘要:
L-[4-C-13]Lysine (2) was synthesized from sodium [2-C-13]acetate (3) and Dellaria's oxazinone 1 as a chiral glycine equivalent. Wittig reaction of the glycinal 7 and C-13-labeled phosphonium ylide 5, prepared from sodium [2-C-13]acetate (3), gave the a, beta-unsaturated ester 8. The ester 8 was converted to the allylic bromide 10. Alkylation of the oxazinone I with 10 proceeded with high diastereoselectivity. Ethanolysis, hydrogenation of the double bond with diimide, removal of the chiral auxiliary, and hydrolysis gave L-[4-C-13]Iysine (2). Copyright (C) 2004 John Wiley Sons, Ltd.
摘要:
L-alpha-(1-Cyclobutenyl)glycine (1-Cbg) was targeted as a potentially translatable analogue of isoleucine and valine and as a useful building block for peptides. An enantioselective synthesis was executed in which the key step was diastereoselective addition of 1-cyclobutenylmagnesium bromide to the sulfinimine 2b derived from (S)-t-butanesulfinimide and tert-butyl glyoxylate. 1-Cbg was found to substitute efficiently for isoleucine and valine, but not leucine, in the translation of green fluorescent protein in vitro.
摘要:
Highly diastereoselective carbon-carbon bond-forming reactions achieved on a variety of sugar templates were found. For example, methyl 6-deoxy-2,3-di-O-(t-butyldimethylsilyl)-alpha-D-glucopyranoside can serve as a versatile and effective chiral auxiliary. Namely, the 1,4-addition reactions to its 4-O-crotonyl ester of some carbon nucleophiles or alkyl radicals proceeded highly diastereoselectively to afford the corresponding adducts. The alkylation of the enolate generated from its 4-O-propionyl ester afforded the alpha-alkylated product with a useful level of stereoselectivity. Furthermore, the Diels-Alder reaction of its 4-O-acryloyl ester with cyclopentadiene afforded an endo-adduct stereoselectively. In the case of the 1,3-dipolar cycloaddition of the acryloyl ester, again the cycloadduct was obtained highly stereoselectively. Some other types of sugar templates prepared from methyl alpha-D-glucopyranoside, alpha-D-mannopyranoside and alpha-D-galactopyranoside were explored to verify their ability to function as chiral templates. In some cases, these templates afforded complementary results in the sense of diastereoselectivity. Methodologies for the removal of the sugar template from the products were developed.