Procedure:  500 mL, 1-neck flask, stirbar, septum, N₂ inlet

                  Dissolved 10.015 g of thiazole I in 250 mL of isopropanol.  Stirred; cooled to 0 C.  Added 10.005 g of LiBH₄.  Removed bath and let stir overnight at rt.  After 16 h, quenched by carefully pouring the reaction mixture into 400 mL of sat. aq. NH₄Cl.  When bubbling had stopped the solution was saturated with NaCl and extracted with EtOAc.  The organic layer was dried over MgSO₄, filtered and the solvent was removed by rotary evaporation.  The product was isolated by flash chromatography on silica gel using EtOAc followed by 1:9 MeOH-EtOAc as eluant.  The product was a clear, colorless oil.

 

¹H NMR (CDCl₃, 400 MHz) d 6.18 (s, ArH), 5.06 (b, NH₂), 3.86 (t, J = 5.7 Hz, ArCH₂), 3.50 (b, OH), 2.76 (m, ArCH₂CH₂). 

 

notes

 

The reduction of esters to alcohols with LiBH₄ is a concerted process whereby an O-B bond is formed as addition of hydride to the carbonyl proceeds.  All four hydrides from BH₄ are available for addition and this complicates the reaction mechanism which is depicted below for a single hydride transfer.  After hydride transfer an elimination of ethoxide must necessarily occur to afford the aldehyde.  A second hydride transfer followed by solvolysis with isopropanol liberates the free hydroxyl and completes the reaction.