Add time:09/28/2019         Source:infona.pl

A two-step synthesis of (R)- and (S)-[ 2 H 1 ]-fluoroacetate (sodium salts) in high enantioselectivity is reported. The synthesis is the development of a previous one in which the enantioselectivity has been increased from ∼38% ee to >95% ee. The improvement in enantioselectivity applied Bio’s methodology, which involved a deoxyfluorination reaction with DAST on either enantiomer of [ 2 H 1 ]-benzyl alcohol, adding TMS-morpholine to the reaction. The additive promotes an S N 2 inversion process, and suppresses a competing non-stereospecific S N 1 reaction course, and as a result significantly improves the stereointegrity of the C–F bond formation. The intermediate [ 2 H 1 ]-benzyl alcohols, [ 2 H 1 ]-benzyl fluorides and the product [ 2 H 1 ]-fluoroacetates as their hexyl esters were separately assayed for their stereochemical integrity, using the Courtieu method. This method involved measuring their 2 H NMR spectra in a chiral matrix of poly-γ-benzyl l-glutamate. The chiral assay demonstrated that there was no significant loss in stereointegrity during the deoxyfluorination reaction and showed that the enantiomers of [ 2 H 1 ]-fluoroacetate were generated with high enantiomeric purity (95% ee).

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