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

                  Dissolved 4.0 mL of phosphonate II in 50 mL of dry THF.  Stirred at rt.  Carefully added 0.988 g of NaH (60% dispersion in mineral oil).  Vigorous gas evolution occurred.  After 45 min, a clear solution resulted which was added to a rt solution of 3.35 mL of ketone I in 25 mL of dry THF using a cannula.  After 16 h, TLC (10:90 MeOH-CH₂Cl₂, UV) showed product spot at Rf 0.45.  The reaction mixture was diluted with water and extracted wth EtOAc.  The organic layer was dried over MgSO₄, filtered and the solvent removed by rotary evaporation. The product was isolated by flash chromatography on silica gel using 10:90 MeOH-CH₂Cl₂ as eluant.  The product was a clear, colorless oil. 

 

¹H NMR (CDCl₃, 300 MHz) d 5.10 (s, CHCN, 1H), 2.62 (m, CHs, 2H), 2.51-2.45 (m, CHs, 4H), 2.40 (m, CHs, 2H), 2.30 (d, J = 1.8 Hz, NCH₃, 3H). 

 

notes

 

Wadsworth-Emmons reagents (alkylphosphonate anions) are useful for the preparation of alkenes from aldehydes and ketones.  The anion is usually generated from the alkylphosphonate by treatment with NaH, n-BuLi or NaOEt.  Because Wadsworth-Emmons reagents react through a true anion, they tend to be more nucleophilic than Wittig reagents which react through a stabilized ylide.  Higher yields of addition products with ketones can often be obtained with Wadsworth-Emmons reagents.

 

Another advantage that Wadsworth-Emmons reagents have is the formation of a water soluble byproduct which is much easier to get rid of than the Ph₃P=O formed in Wittig reactions.