Leucine t-butyl ester

The product from Step 3 (179 mmol) was added to a solution of L-leucine t-butyl ester isocyanate (179 mmol) dissolved in 300 ml DMF, stirred 2 hours at ambient temperature, then stood overnight. The solvent was removed, the residue treated with heptane, and the mixture stirred at ambient temperature 2 hours. The precipitate was filtered and the product isolated in 69% yield. 

The preparation of L-leucine t-butyl ester isocyanate is described (1). 

L-Leucine t-butyl ester is a highly effective chiral auxiliary for the diastereoselective and enantioselective additions of Grignard reagents to cyclo-alkene carboxaldehydes as their imines (Scheme 46). Of particular interest are the stereoselectivities observed on alkylation of the resulting chiral enolates. 

Reaction of a/3-unsaturated aldehydes with optically active t-leucine t-butyl ester gives chiral a/3-unsaturated aldimines (46). 1,4-Addition of Grignard reagents to these aldimines yields, after hydrolysis, -substituted aldehydes of high optical... 

The first approach investigated was the L-leucine approach (Hoekstra et al., 1997), as shown in Scheme 16.14, in which L-leucine was converted to the bromoester 49. The bromide was displaced with excess diethyl sodiomalonate to give triester 50 in good yield. The t-butyl ester was deprotected by formic acid treatment and the resulting acid... 

A method based on the DKR of 4-substituted-2-phenyloxazolin-5-one has been apphed to the large-scale synthesis of N-benzoyl-t-t-leucine-butyl ester 19, an important non-natural amino acid intermediate of several biomimetic peptides. The procedure is based on the alcoholysis of 4-t-butyl-2-phenyloxazoUn-5-one 18 with -butanol catalyzed by the lipase from Mucor miehei (Scheme 13.15) [42]. The unreactive enantiomer is racemized in situ by a base-catalyzed reaction. The... 

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