'Phospha-variations' on the themes of Staudinger and Wittig: phosphorus analogs of Wittig reagents

The Wittig and Aza-Wittig reactions have undergone tremendous development o ver the past 50 years in light of their potential in organic synthesis to c onstruct carbon-carbon and carbon -nitrogen double bonds. In contrast, the development of the analogous phospha-Wittig reaction has only seen progress over the last 12 years. A phospha-Wittig process is one that uses phosphay lides to convert carbonyl compounds to new materials possessing phosphorus- carbon double bonds (phosphaalkenes). The phospha-Wittig reaction has evolv ed from initial work involving metal-assisted phospha-Wittig reactions, to phospha-Wittig reactions of terminal phosphinidene complexes to, more recen tly, free phosphanylidene-sigma (4)-phosphoranes as phospha-Wittig reagents . The major developments in the phospha-Wittig reaction are highlighted and divided into these three methodologies. The complementary nature and the d ifferences between the three approaches is also discussed. Finally, wherein applicable, comparisons between the Wittig reaction and the phospha-Wittig reaction are presented. (C) 2000 Elsevier Science B.V. All rights reserved .