A new and easy synthesis of chiral bifunctional organic catalysts obtained by the combination of (S)-t-leucine-derivatives with (1R,2R)-trans-1,2-diamino-cyclohexane was developed. A few compounds, representatives of a class of organocatalysts containing a thiourea group and a tertiary amino group connected through a chiral backbone, have been successfully synthesized. The catalytic behaviour of such bifunctional chiral molecules, either neutral or protonated species, was investigated in the addition of acetylacetone to β-nitrostyrene as a model reaction. Using the best conditions, high yields and enantioselectivities of up to 85% were obtained. The same metal free catalysts were then employed in the addition of activated nucleophiles to imines: in the reaction of 1,3-diketones with N-CBz imines, the products were isolated in up to 61% ee, while in the reaction with diethyl malonate enantioselectivities up to 71% were reached.
Stereoselective nucleophilic addition to imines catalyzed by chiral bifunctional thiourea organocatalysts / A. Puglisi, M. Benaglia, R. Annunziata, D. Rossi. - In: TETRAHEDRON-ASYMMETRY. - ISSN 0957-4166. - 19:19(2008 Oct 06), pp. 2258-2264. [10.1016/j.tetasy.2008.09.030]
Stereoselective nucleophilic addition to imines catalyzed by chiral bifunctional thiourea organocatalysts
A. PuglisiPrimo
;M. BenagliaSecondo
;R. AnnunziataPenultimo
;
2008
Abstract
A new and easy synthesis of chiral bifunctional organic catalysts obtained by the combination of (S)-t-leucine-derivatives with (1R,2R)-trans-1,2-diamino-cyclohexane was developed. A few compounds, representatives of a class of organocatalysts containing a thiourea group and a tertiary amino group connected through a chiral backbone, have been successfully synthesized. The catalytic behaviour of such bifunctional chiral molecules, either neutral or protonated species, was investigated in the addition of acetylacetone to β-nitrostyrene as a model reaction. Using the best conditions, high yields and enantioselectivities of up to 85% were obtained. The same metal free catalysts were then employed in the addition of activated nucleophiles to imines: in the reaction of 1,3-diketones with N-CBz imines, the products were isolated in up to 61% ee, while in the reaction with diethyl malonate enantioselectivities up to 71% were reached.File | Dimensione | Formato | |
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