Wittig Reaction: Role of Steric Effects in Explaining the Prevalent Formation of Z Olefin from Nonstabilized Ylides

Abstract

For understanding the mechanism involved in the Wittig reaction, it is important to know the factors which influence the stability of 1,2-oxaphosphetane intermediates with pentacoordinate phosphorus; in these intermediates, the steric factor plays a predominant role. Studying the Wittig reaction between nonstabilized ylides and different aldehydes, we noted that the stereochemical outcome driving toward Z-olefin formation was influenced only by different steric factors. The proposed mechanism differs from those previously reported because it underlines the fundamental role of the two cis/trans oxaphosphetane intermediates with the oxygen atom in equatorial position.

GRAPHICAL ABSTRACT

Keywords:

• Oxaphosphetanes
• phosphorylation
• ³¹P NMR spectroscopy
• E-olefin
• Z-olefin

Acknowledgments

This work was financially supported by the Alma Mater Studiorum, Università di Bologna (RFO funds) and by the MIUR (PRIN Project 2007: “New frontiers in the synthesis, reactions and applications of compounds containing heteroatoms”).