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.
Titolo: | Stereoselective nucleophilic addition to imines catalyzed by chiral bifunctional thiourea organocatalysts |
Autori: | PUGLISI, ALESSANDRA (Primo) BENAGLIA, MAURIZIO (Secondo) ANNUNZIATA, RITA MARIA (Penultimo) |
Settore Scientifico Disciplinare: | Settore CHIM/06 - Chimica Organica |
Data di pubblicazione: | 6-ott-2008 |
Rivista: | |
Tipologia: | Article (author) |
Digital Object Identifier (DOI): | 10.1016/j.tetasy.2008.09.030 |
Appare nelle tipologie: | 01 - Articolo su periodico |
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