Phosphonamides, Wittig reaction

The phosphonamide route has some advantages over the Wittig reaction. The reagents are readily prepared and potentially cheaper. The products are readily isolated (separation from triphenylphosphine oxide is sometimes troublesome). The intermediate /3-hydroxyphosphonic acid amides are readily purified. There is more opportunity to control the geometry and position of the double bond. 

Asymmetric Wittig-Homer reactions Wittig-Horner reactions have usually involved phosphine oxides, phosphonates, or phosphonamides. Highly enantioselective ole-finations have now been achieved by use of this chiral phosphonamidate 1. Thus the anion (/-BuLi) reacts with 4-/-butylcyclohexane to form 2 in >98% de. Elimination with trityl triflate/2,6-lutidine provides the alkylidene 3 with essentially complete stereospecificity. The reaction was shown to be applicable to a variety of 4-aIkylcyclohexanones. 

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