Catalytic Diastereo- and Enantioselective Synthesis of 2-Imidazolinones (original) (raw)

Synthesis of Novel Chiral (Thio)ureas and Their Application as Organocatalysts and Ligands in Asymmetric Synthesis

Australian Journal of Chemistry, 2008

The synthesis of novel chiral (thio)ureas 1-10 and 14-26 is described. These (thio)ureas incorporate chiral auxiliaries derived from (R)-or (S)-α-phenylethylamine, (R)-phenylglycine, or (1R,2S)-ephedrine. The phenylethyl group in compounds 1-10 and 21-24 adopts a particular orientation in the molecular structure as a consequence of 1,3-allylic strain with the (thio)carbonyl group. Ureas 1-10 were tested as Lewis basic organocatalysts in epoxide ring opening and in aldolic condensation, and it was found that the tetrasubstituted urea (R,R)-2 afforded the best results in terms of reaction yields. (Thio)ureas 20-26 were examined as ligands in the enantioselective diethylzinc addition to benzaldehyde, observing that C 2 -symmetric chiral urea (R,S,R,S)-20 provides the expected carbinol in nearly quantitative yield and in up to 62% enantiomeric excess.

One-Pot Synthesis of Polyfunctionalized Cyclic Urea Derivatives

Organic Letters, 2003

Unexpectedly, imidazolidin-2-ones are easily obtained from -keto esters upon treatment with tert-butyl nosyloxycarbamate and calcium oxide under mild conditions. The structure of the product was established by X-ray crystallography.

2-Unsubstituted Imidazole N-Oxides as Novel Precursors of Chiral 3-Alkoxyimidazol-2-ylidenes Derived from trans-1,2-Diaminocyclohexane and Other Chiral Amino Compounds

Molecules

'Desymmetrization' of trans-1,2-diaminocyclohexane by treatment with α,ω-dihalogenated alkylation reagents leads to mono-NH 2 derivatives ('primary-tertiary diamines'). Upon reaction with formaldehyde, these products formed monomeric formaldimines. Subsequently, reactions of the formaldimines with α-hydroxyiminoketones led to the corresponding 2-unsubstituted imidazole N-oxide derivatives, which were used here as new substrates for the in situ generation of chiral imidazol-2-ylidenes. Upon O-selective benzylation, new chiral imidazolium salts were obtained, which were deprotonated by treatment with triethylamine in the presence of elemental sulfur. Under these conditions, the intermediate imidazol-2-ylidenes were trapped by elemental sulfur, yielding the corresponding chiral non-enolizable imidazole-2-thiones in good yields. Analogous reaction sequences, starting with imidazole N-oxides derived from enantiopure primary amines, amino alcohols, and amino acids, leading to the corresponding 3-alkoxyimidazole-2-thiones were also studied.

1,3-Dipolar cycloaddition of C-(2-thiazolyl)nitrones to chiral acrylates. Synthesis of enantiopure α-amino-2-alkylthiazoles and 5-formylpyrrolidin-2-ones

Tetrahedron, 1997

The 1,3-dipolar cycloaddition of thiazolyl nitrones with chiral acrylates has been studied. The use of the Oppolzer's camphor sultam as chiral inductor provided isoxazolidines with excellent regio-and diastereoselectivities and good asymmetric induction. The cycloadducts were converted into homochiral cc-amino-2-alkylthiazoles and 5-(2-thiazolyl)-3-hydroxy-2-pyrrolidinones. The latter compounds were precursors of highly functionalized pyrrolidines by the aldehyde unmasking from the thiazole ring and subsequent reactions of the formyl group. © 1997 Elsevier Science Ltd. All rights reserved.