... Tetrahedron: Asymmetry. Volume 12, Issue 21, 26 November 2001, Pages 2989–2997. ... Cleavage of the amide of 12 with 20% NaOH in EtOH at 50°C smoothly afforded (S,S)-4 in 93% yield and protection of (S,S)-4 with Boc 2 O afforded 13 in 98% yield. ...