Self-consistent sequential’ reactions

Fluoropyruvaldehyde N,S-ketah (R)-32 can be prepared in good yields (up to 88%) and e.e. s (up to 82%) from a-(fluoroalkyl)-p-sulfmylenamines (7 )-2-19a-c (Scheme 9), through an unprecedented self-immolative tandem sequential process (34,35), consisting in a Pummerer reaction promoted by TFAA (.step 1) that provides the intermediate a-trifluoroacetoxy A -Cbz imine 36, followed by a 1,2-migration of the / -tolylthio group (step 2), triggered by addition of silica gel or aqueous base. 

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