Mitsunobu reaction ether-bond forming

It is interesting to note that the inventors of (/ )-K-13675, in the first reported synthetic approach, targeted the racemic compound 1, and contracted separation of the enantiomers by preparative chiral chromatography to the expert company in this field, Diacel Chemical Indistries Ltd. [37]. Continuing scale-up investigations, the authors succeeded in replacing the Mitsunobu method, in the ether bond-forming reaction, by the technically much more simple use of triflate 21, prepared on a kg scale from (5)-n-butyl-2-hydroxybutanoate 20 (Scheme 3.8) [38]. 

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