Byrne, Peter A.Peter A.ByrneHigham, Lee J.Lee J.HighamMcGovern, PádraicPádraicMcGovernGilheany, Declan G.Declan G.Gilheany2013-11-192013-11-192012 Elsev2012-12Tetrahedron Lettershttp://hdl.handle.net/10197/4938Wittig reaction products of keto-stabilised ylides with ortho-substituted benzaldehydes are found to show significantly higher than expected Z-alkene content (up to 50%) compared to analogous reactions of the same ylides with benzaldehyde itself. A cooperative effect is seen whereby the unusual Z-content is further augmented if the ylide bears greater steric bulk in the α′-position. These results are consistent with our previous observations on reactions of all ylide types with aldehydes bearing a β-heteroatom. Significantly, the cooperative effect, previously seen only with semi-stabilised ylides, has now been extended to stabilised ylides. Both the anomalous increase in Z-content and the cooperative effect can be rationalised within the [2+2] cycloaddition mechanism of the Wittig reaction.enThis is the author’s version of a work that was accepted for publication in Tetrahedron Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Tetrahedron Letters (Volume 53, Issue 49, 5 December 2012, Pages 6701–6704) Elsevier B.V.Wittig reaction mechanismKeto-stabilised phosphonium ylideortho-Substituted benzaldehydesKinetic control in Wittig reactionsZ-Alkene[2+2] CycloadditionJournal Article53496701670410.1016/j.tetlet.2012.09.1232013-10-10https://creativecommons.org/licenses/by-nc-nd/3.0/ie/