Phosphonated trialkylphosphine

Scheme 2.30 Synthesis of a phosphonated trialkylphosphine and examples of triarylphos-phines with phosphonate groups.

Ylids are usually prepared from triphenylphosphine, but other triarylpho-sphines, trialkylphosphines, and triphenylarsine " have also been used. The Wittig reaction has also been carried out with other types of ylids, the most important being prepared from phosphonates " ... 

The reaction of trialkylphosphines, especially triphenylphosphine, with alkyl halides is particularly useful since the resultant phosphonium salts are easily converted to the phosphonium ylid on treatment with a suitable base (sec. 8.8r kk Ylids are, of course, the reactive species in the well-known Wittig olefination reaction, which will be discussed in section 8.8.A.i. A related Sn2 process involves reaction of a trialkylphosphite with an alkyl halide, the Arbuzov reaction (sometimes called the Michaelis-Arbuzov reaction). Triethylphos-phite (70) reacts with iodomethane to give the phosphonium salt, 71. Heating generates the monoalkyl phos-phonic ester (72). This type of phosphonic ester can be converted to an ylid and used in the well-known Horner-Wadsworth-Emmons oiefination (sec. 8.8.A.iii). 

---