Procedure:  50 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Dissolved 0.413 g alcohol I in 15 mL of dry CH₂Cl₂.  Stirred at rt and added 0.533 g of (S)-MPAA (II) and 0.434 g of DCC followed by 0.241 g of DMAP.  After 3 h TLC still showed unreacted alcohol.  Added 0.080 g of (S)-MPAA.  Stirred 20 min.  TLC still showed unreacted alcohol.  Added 0.065 g DMAP.  Stirred 20 min.  TLC still showed unreacted alcohol.  Added 0.087 g of DCC.  After 10 min TLC showed no more alcohol.  Next time use more DCC to start with.  The solvent was removed from the reaction mixture by rotary evaporation  The residue was triturated in Et₂O, filtered through Celite and the solvent was removed by rotary evaporation.  The product was isolated by flash chromatography on silica gel using 20:80 Et₂O-hexanes. 

 

¹H NMR (CDCl₃, 300 MHz) d 7.44-7.29 (m, C₆H₅), 5.62 (ddd, J = 17.0, 10.6, 6.1 Hz, H2), 5.26 (m, H3), 4.97 (ddd(apparent t), J = 10.6, 1.3 Hz, cis H1), 4.91 (ddd(apparent t), J = 17.2, 1.3 Hz, trans H1), 4.75 (s, CHOCH₃), 3.40 (s, OCH₃), 1.58-1.22 (m, CH₂s), 0.86 (bt, J = 6.7 Hz, CH₃). 

notes

 

The reaction follows one of two possible pathways as illustrated below.

 

Forming the mandelate of a non-racemic alcohol is a useful way to determine the optical purity of the alcohol.  The introduction of a second stereocenter allows for the observation of both pairs of diastereomers in the ¹H NMR.  Since both (R) and (S)-MPAA are commercially available, both diastereomers are accessible.  Having each diastereomer on hand for NMR analysis becomes important when the chemical shifts of either diastereomer are unknown. 

In this reaction, four diastereomers are possible with the use of both (R) and (S)-MPAA and provided the ee of the starting alcohol is less than 100%.  A and B are enantiomers and will show a different NMR spectum from that of C and D.