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Co-operative ortho-effects on the Wittig reaction. Interpretation of stereoselectivity in the reaction of ortho-halo-substituted benzaldehydes and benzylidenetriphenylphosphoranes

✍ Scribed by Eoin C Dunne; Éamonn J Coyne; Peter B Crowley; Declan G Gilheany

Publisher
Elsevier Science
Year
2002
Tongue
French
Weight
87 KB
Volume
43
Category
Article
ISSN
0040-4039

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✦ Synopsis

The E/Z ratios of the stilbenes 1 formed in the Wittig reaction of ortho-halo substituted benzyltriphenylphosphonium salts 2 and benzaldehydes 3 were determined. It was found that there is a co-operative effect of one ortho-halo group on each of the two reacting partners which increases Z-selectivity, but two such groups on the same reactant gives high E-selectivity. The effects are strong enough to be preparatively significant in certain cases and can be interpreted within the modern framework of the Wittig mechanism established by Vedejs and co-workers.

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