A New Synthetic Method for the Preparation of α,β-Didehydroamino Acid Derivatives by Means of a Wittig-Type Reaction. Syntheses of (2S,4S)- and (2R,4R)-4-Hydroxyprolines.

Ethyl N-Boc- and N-Z-α-tosylglycinates were reacted with a variety of aldehydes in the presence of tributylphosphine and a base to afford the corresponding α,β-didehydroamino acid derivatives with high (Z)-selectivity in good yields. Moreover, ethyl (4S)- and (4R)-2-(N-Boc-amino)-4,5-isopropylidenedioxy-2-pentenoates prepared by the present method were converted to (2S, 4S)- and (2R, 4R)-4-hydroxyprolines, respectively.