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Please login to access the full content or check if you have access via Method 3: E-Selective Alkenation with Ylides Bearing Substitutents Other Than Triphenylphosphine

DOI: 10.1055/sos-SD-047-00004

Schobert, R.; Hölzel, C.; Barnickel, B.Science of Synthesis, (20104752.

Extensive studies in the 1960s revealed that alkyl substitutents attached to the phosphorus atom in phosphonium salts decrease its acidity when compared to triphenylphosphine. Since phosphonium salts and their ylides can be regarded as a Brønsted acid/base system,[‌83‌] P-alkyl substitution is a way to increase the basicity and nucleophilicity of the corresponding ylides.[‌370‌,‌385‌‌387‌] Bestmann and co-workers showed that ylides bearing cyclohexyl instead of phenyl groups at the phosphorus atom lead to pure E-alkenes.[‌370‌] This finding was subsequently rationalized theoretically[‌253‌,‌388‌,‌389‌] and has been confirmed by density functional theory calculations.[‌390‌] Examples of ylides bearing groups other than triphenylphosphine are shown in Scheme 38.

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