Amino Acids

Aldrich ChemFiles 2007, 7.9, 10.

Aldrich ChemFiles 2007, 7.9, 10.

Barbas and co-workers found the proteinogenic amino acid tryptophan (93660) to be an excellent organocatalyst for the Mannich reaction of hydroxyacetone with a variety of imines performed in DMF (Scheme 1). The desired anti amino alcohols were obtained in good yields with excellent diastereoselectivities (up to >19:1) and enantioselectivities (90–98% ee) in most cases.1 Similarly, t-butyl protected threonine (20644) catalyzed the aldol reaction of hydroxyacetone and various aldehydes in NMP to give the corresponding syn-aldol adducts in high yields and good to excellent enantio- and diastereoselectivities (Scheme 2).1

Scheme 1

Scheme 2

Professors Marc Snapper and Amir Hoveyda at Boston College have recently reported2 the development of an amino-acidbased small molecule (680826) capable of promoting asymmetric monosilylation of meso-1,2-diols (Scheme 3). The catalyst is compatible with a variety of silyl chlorides and generally provides enantioselectivities above 88%, and the reactions do not require rigorous exclusion of air or moisture. Furthermore, the catalyst can be easily recovered in near-quantitative yield and subsequently reused with identical efficiency. This catalyst greatly increases the efficiency with which optically enriched molecules can be prepared.

Scheme 3

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  1. Ramasastry, S. S. V.; Zhang, H.; Tanaka, F.; Barbas, C. F., III J. Am. Chem. Soc. 2007, 129, 288.
  2. Zhao, Y.; Rodrigo, J.; Hoveyda, A. H.; Snapper, M. L. Nature 2006, 443, 67.

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