Anomalous Z-isomer content in Wittig reaction products from keto-stabilised ylides with ortho-heteroatom substituted benzaldehydes
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Byrne, Peter A.
Higham, Lee J.
Gilheany, Declan G.
Wittig 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.
Wittig reaction mechanism , Keto-stabilised phosphonium ylide , ortho-Substituted benzaldehydes , Kinetic control in Wittig reactions , Z-Alkene , [2+2] Cycloaddition
Byrne, P. A., Higham, L. J., McGovern, P. and Gilheany, D. G. (2012) 'Anomalous Z-isomer content in Wittig reaction products from keto-stabilised ylides with ortho-heteroatom substituted benzaldehydes', Tetrahedron Letters, 53(49), pp. 6701-6704. doi: 10.1016/j.tetlet.2012.09.123