Procedure:  250 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Dissolved 1.66 mL of propargyl alcohol (I) in 50 mL of dry CH₂Cl₂.  Stirred at rt.  Added 3.15 mL of DHP followed by 0.725 g of PPTS.  After 2.5 h the reaction was quenched with sat. aq. NaHCO₃ and extracted with Et₂O.  The organic layer was dried over MgSO₄, filtered and the solvent was removed by rotary evaporation.  The product was isolated by Kugelrohr distillation (70 C, aspirator).  The product was a clear, colorless oil. 

 

¹H NMR (CDCl₃, 400 MHz) d 4.80 (t, J = 3.3 Hz, OCHRO), 4.28, 4.21 (dABq, J = 15.6, 2.4 Hz, H1), 3.82 (m, OCH₂), 3.52 (m, OCH₂), 2.39 (t, J = 2.4 Hz, H3), 1.85-1.51 (m, CH₂s)

 

notes

 

PPTS is a weak acid and acts as a mild catalyst for the tetrahydropyranylation of alcohols (see Miyashita, N.; Yoshikoshi, A.; Grieco, P.A.  J. Org. Chem. 1977, 42, 3772).  Removal of the THP group can also be affected with PPTS in ethanol. 

 

This mechanism for this protection involves a simple acid catalyzed acetal formation.