A short and efficient synthesis of L-5,5,5,5',5',5'-hexafluoroleucine from N-Cbz-L-serine.

[reaction: see text] 5,5,5,5',5',5'-Hexafluoroleucine (6), a fluorous analogue of leucine, is of considerable interest as a building block in the design of fluorous proteins and peptides. We report a short and efficient synthesis of 6, which is obtained from N-Cbz-L-serine (1) in 50% overall yield, 99% enantiomeric excess, and in multigram quantities. Key steps are addition of a serine-derived organozincate to hexafluoroacetone to construct the hexafluoroleucine side chain, followed by radical-mediated deoxygenation of the resulting tertiary alcohol.