Enantioselective Strecker Reaction of Phosphinoyl Ketoimines Catalyzed by in Situ Prepared Chiral N,N′-Dioxides Jinglun Huang,† Xiaohua Liu,† Yuehong Wen,† Bo Qin,† and Xiaoming Feng*,†,‡ Key Laboratory of Green Chemistry & Technology (Sichuan UniVersity), Ministry of Education, College of Chemistry, Sichuan UniVersity, Chengdu 610064, China, and State Key Laboratory of Biotherapy, West China Hospital, Sichuan UniVersity, Chengdu 610041, China
[email protected] ReceiVed September 28, 2006
The enantioselective Strecker reaction of N-diphenylphosphinoyl ketoimines has been achieved by use of in situ prepared chiral N,N′-dioxide catalyst from L-piperidinamide 3f and m-chloroperoxybenzoic acid (m-CPBA). Excellent yields (up to 99%) and high enantioselectivities (up to 92% ee) were obtained. In particular, in situ prepared catalyst with readily available chiral material made the procedure more convenient. Moreover, the L-piperidinamide 3f-derived N,N′-dioxide 9 could be recycled and reused at least five times without any loss of either catalytic activity or enantioselectivity.
Introduction The Strecker reaction is one of the most attractive methods for the synthesis of R-amino acids and their derivatives.1 Effective catalytic asymmetric cyanation of various aldimines has been achieved, leading to efficient formation of monosubstituted chiral R-amino nitriles.2 However, relatively fewer systems have been developed for catalytic asymmetric cyanation of ketoimines, which is very useful for the generation of quaternary R-amino acids. Reported methods include metal† ‡
Key Laboratory of Green Chemistry & Technology. State Key Laboratory of Biotherapy.
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J. Org. Chem. 2007, 72, 204-208
Published on Web 12/07/2006
Strecker Reaction of Phosphinoyl Ketoimines
FIGURE 1. Catalysts evaluated in this study. TABLE 1. Asymmetric Strecker Reaction Catalyzed by Various
TABLE 2. Solvent and Catalyst Loading Effects on the Strecker
Catalystsa
Reaction of Ketoimine 7aa
catalyst entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14
precursor (mol %) 1 (20) 2 (20) 3a (20) 3b (20) 3c (20) 3d (20) 3e (20) 3f (20) 3g (20) 3h (20) 4 (20) 5 (20) 6a (20) 6b (20)
catalyst m-CPBA mol %
conversion,b %
ee,c %
entry
0 40 40 40 40 40 40 40 40 40 40 40 40 40
28 29 56 15 45 20 50 64 28 10 95
