O- Trifluoromethanesulfonyl L-Lactic Acid Derivatives

The enhanced leaving ability of the triflate group allows Sn2 substitution reactions to occur at lower temperatures and over shorter periods of time relative to other leaving groups. When 

Preparatively, ( S)-189 is available by the action of triflic anhydride on 2 in the presence of pyridine [70]. It is fairly stable, and can be kept for months at 0-10 °C [71]. 

With respect to reactivity, 189 reacts smoothly with a variety of primary and secondary amines at room temperature to give D-amino acid esters 190 in 75—93% yield [71]. 

Even the relatively non-nucleophilic 2,6-dimethylaniline reacts with the methyl 2-trifloxy ester analog 191 (17 h at room temperature) to give the oW-arylalanine ester 192 in high yield. Acylation with methoxyacetyl chloride gives the fungicide Ridomil (193) [70]. 

Displacement of the triflate group of 191 with er -butylcarbazate is achieved within two hours at 0 °C to furnish protected 2-hydrazinyl ester 100 with total inversion of the asymmetric center ( 95% ee) [35]. Compare this with the identical reaction using nosylester 98, which takes 5 days to complete and gives 100 with only 72% ee (see Section 1.2). 

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