Synthesis 2011(12): 1918-1925  
DOI: 10.1055/s-0030-1260038
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Amino Acid Catalysed Aldol Reactions in Cyclic Carbonate Solvents

Maria Morcillo, Michael North*, Pedro Villuendas
School of Chemistry and University Research Centre in Catalysis and Intensified Processing, Bedson Building, Newcastle University, Newcastle-Upon-Tyne, NE1 7RU, UK
Fax: +44(191)2226929; e-Mail: Michael.north@ncl.ac.uk;
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Publikationsverlauf

Received 14 March 2011
Publikationsdatum:
10. Mai 2011 (online)

Abstract

Ethylene and propylene carbonates are shown to be alternative polar aprotic solvents for cross-aldol reactions catalysed by the primary amino acids (S)-phenylalanine and (S)-tryptophan. In contrast to the corresponding proline-catalysed reactions, both enantiomers of these naturally occurring, primary amino acids are available at low cost. The optimal catalyst and solvent combination needs to be determined on a substrate by substrate basis.

4

The current UK Aldrich catalogue price for (S)-proline is £ 0.31/g whilst the cost of (R)-proline is £ 13.32/g (prices based on the largest available quantities). In contrast, the S-enantiomers of phenylalanine and tryptophan are available for £ 0.28/g and £ 0.54/g, respectively and the R-enantiomers are available for £ 2.53/g and £ 2.11/g, respectively. Thus, (R)-proline is 43 times more expensive than (S)-proline, whereas (R)-phenylalanine is only 9 times as expensive as (S)-phenylalanine and (R)-tryptophan is only 4 times as expensive as (S)-tryptophan.