Recently, the asymmetric Michael addition mediated by the derivatives of L-prolinol has been a big hit in the field of asymmetric synthesis. However, the protection of the amino group of L-prolinol is a key step and often involved in the synthesis of L-prolinol derivatives. Thus, the stability of Cbz or Boc protected L-prolinol derivatives is investigated. It was found that when the hydroxyl group of Boc protected L-prolinol is replaced by easily leaving group, it is unstable and cyclization proceeds effectively to give γ-butyrolactone at 67 ℃|however, Cbz protected L-prolinol derivatives are more stable, similar cyclization will happen at 140 ℃ in the presence of triethylamine.

Key words: derivative of prolinol, stability, Cbz protection, Boc protection, cyclization