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DOI: 10.1055/s-2008-1078010
An Improved Lanthanum Catalyst System for Asymmetric Amination
Contributor(s):Hisashi Yamamoto, Pingfan LiThe University of Tokyo, Japan
An Improved Lanthanum Catalyst System for Asymmetric Amination: Toward a Practical Asymmetric Synthesis of AS-3201 (Ranirestat)
Org. Lett. 2008, 10: 2725-2728
Publication History
Publication Date:
22 August 2008 (online)
Key words
lanthanum - asymmetric amination - peptide ligands - cooperative effect
Significance
Catalytic asymmetric amination using azo compounds as nitrogen source is becoming a versatile method for the preparation of various useful building blocks. This paper described the development of a practical protocol based on further optimization of a previously reported lanthanum catalyst system. A one-hundred gram scale experiment nicely showcased the robust nature of this reaction.
Comment
Practicability is still not so easy for catalytic asymmetric reactions. This paper is a nice showcase for this difficult challenge. The use of lanthanum nitrate hydrate instead of lanthanum triisopropoxide as metal source not only alleviated the previous problems of cost and reproducibility, but also prompted investigation of the effect of various base additives, which led to the identification of tert-butyl ester of d-valine as an optimal amine. Such studies further contributed to the understanding of the critical species in the pre-catalyst.