No abstract

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 Eand Z-selectivity has been achieved, despite the E/Z-directivity of the carbonyl reagent and of the residue linked to the phosphorane moiety.

Today, there is a big market for steroidal hormones as well as for their derivatives. This review traces the development in steroidal production from the first milligram-scale isolation of the products to their semi-synthesis from sapogenins, their total synthesis and finally their microbial enzymatic preparation from phytosterols.

Esters, acyloximes, amides and acid anhydrides have been prepared from the respective carboxylic acids, oximes, amines and alcohols by the use of the reagent combination BrCCl 3 -PPh 3 . The reactions obviate the handling acyl halides or more aggressive reagents PCl 3 , POCl 3 , or SOCl 2 . Furthermore, the environmentally hazardous CCl 4 used in Appel-type reactions is replaced with BrCCl 3 , a reagent of less environmental concern.

Benzamides were converted into benzonitriles with BrCCl 3 -PPh 3 -Et 3 N in CH 2 Cl 2 in an Appel-type reaction. Benzaldoximes could be transformed to benzonitriles under identical conditions. It was found that the reaction system BrCCl 3 -(2 equiv.)PPh 3 was also suitable for these transformations with PPh 3 replacing Et 3 N.