New Synthetic Routes toward Enantiopure (2S,3R,4R)-4-Hydroxyisoleucine by 1,3-Dipolar Cycloaddition of a Chiral Nitrone to C4 Alkenes.

1,3-Dipolar cycloaddition reaction of a chiral nitrone derived from (-)-menthone to E/ Z mixtures of crotonaldehyde or ( Z)-but-2-en-1,4-diol opens, by simultaneous creation of three contiguous asymmetric centers, new access to enantiopure (2 S,3 R,4 R)-4-hydroxyisoleucine, respectively in 13% (7 steps) and 34% (6 steps) overall yield. [ABSTRACT FROM AUTHOR]