·      

Other phosphines may be used for the reaction. But they should not contain a proton that could be abstracted as is the proton on the halide coupling partner, as a mixture of desired and undesired ylides would be formed.

If the halide contains an electron withdrawing group, the negative charges in the ylide is delocalized, decreasing its nucleophilicity and reactivity. Aldehydes may still react, but ketones likely will not.

Examples:

B. J. Neubert, B. B. Snider, Org. Lett. 2003 , 5 , 765.

R. K. Boeckman, Jr., T. R. Aless, J. Am. Chem. Soc. 1982 , 104 , 3216.

S. P. Chavan, R. K. Kharul, R. R. Kale, D. A. Khobragade, Tetrahedron 2003 , 59 , 2737.

5.4.2 Wittig Indole Synthesis

Indoles are important structural unit and found in numerous natural product and biologically important compounds. Thus, the construction of the indole structural framework remains in organic synthesis. Anilides having memthylphosphonium salt at their ortho position can be converted into indoles in the presence of base (Scheme 3). The reaction is called Wittig indole synthesis.

Scheme 3