A detailed route for the synthesis of the "S" enantiomer of 4-TIPS-3-butyn-2-ol in 90% enantiomeric purity by reduction of the ynone precursor by the Noyori catalytic system was reported by Marshall et al. The ease of catalyst preparation, operational simplicity and potential for scale up, prompted the use of this hydrogenation process for the synthesis of (R)-4-TIPS-3-butyn-2-ol under the conditions of Marshall et al. The reduction of the 4-TIPS-3-butyn-2-one with ca. 1 mol % of the Noyori chiral Ru catalyst in isopropyl alcohol was scaled up to a 25 g scale (than the reported scale of 5 g), proceeded rapidly to afford the (R)-4-TIPS-3-butyn-2-ol with little erosion of ee (80% ee).
The catalyst preparation and the asymmetric reduction procedure reported in this article is reproducible although one might want to perform it on medium scale to retain the higher ee’s as reported. The optically active alcohol was conveniently isolated by distillation under reduced pressure as reported.