Wittig- and Horner-Wadsworth-Emmons-olefination reactions with stabilised and semi-stabilised phosphoranes and phosphonates under non-classical conditions

Developments in the Wittig and Horner-Wadsworth-Emmons (HWE)-olefination of aldehydes and ketones with stabilised phosphoranes or phosphonates provide opportunities for multicomponent reactions and for reactions with greatly reduced solvent requirements. The in situ preparation of phosphonium salts, phosphoranes or phosphonates and carrying out the reaction and product workup in a biphasic medium can greatly facilitate the reactions. Microwave irradiation and ultrasonication can shorten reaction times considerably. Wittig and HWE reactions have also been carried out in the solid phase, with either polymer-bound reagents or in Wittig reactions with reagents adsorbed on silica or alumina. Good E- and Z-selectivity has been achieved, despite the E/Z-directivity of the carbonyl reagent and of the residue linked to the phosphorane moiety.