A Highly Enantioselective Amino Acid-Catalyzed Route to Functionalized α-Amino Acids
Armando Córdova, Wolfgang Notz, Guofu Zhong, Juan M. Betancort and Carlos F. Barbas III*
*The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Rd., La Jolla, California 92037, Email: carlosscripps.edu
A. Cordova, W. Notz, G. Zhong, J. M. Betancort, C. F. Barbas, III, J. Am. Chem. Soc., 2002, 124, 1842-1843.
DOI: 10.1021/ja017270h (free Supporting Information)
Proline-catalyzed Mannich-type reactions of N-PMP-protected α-imino ethyl glyoxylate with a variety of unmodified ketones provided functionalized α-amino acids in high yields with excellent regio-, diastereo-, and enantioselectivities. In reactions involving ketone donors where diastereoisomeric products could be formed, two adjacent stereogenic centers were created simultaneously upon carbon-carbon bond formation with complete syn-stereocontrol. Reactions were typically performed using 20 vol-% of the donor ketone and 20 mol-% proline catalyst, however, reduction of the donor ketone used to 2 eq. and reduction of catalyst loading to 5 mol-% provided the desired products without loss in yield or enantioselectivity.
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H. Zhang, M. Mifsud, F. Tanaka, C. F. Barbas, III, J. Am. Chem. Soc., 2006, 128, 9630-9631.