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47.1.1.1.4.1 Method 1: The Schlosser Modification of the Wittig Alkenation

DOI: 10.1055/sos-SD-047-00004

Schobert, R.; Hölzel, C.; Barnickel, B.Science of Synthesis, (20104749.

In 1966 Schlosser and Christmann reported the first example of a highly E-selective Wittig alkenation using unstabilized ylides.[‌345‌] This protocol later came to be known as the WittigSchlosser reaction or the Schlosser modification of the Wittig alkenation.[‌11‌,‌374‌,‌375‌] An unstabilized ylide 102, prepared from the corresponding phosphonium salt and an organolithium base (PhLi or BuLi) containing additional lithium bromide, is treated with an aldehyde at 78°C. The resulting mixture of erythro- and threo-betaines 103 is deprotonated by a second equivalent of the same lithium base at 30°C to give the lithiated betaines 104A and 104B with the latter prevailing in the equilibrium. Reprotonation by addition of anhydrous hydrochloric acid in diethyl ether or tert-butyl alcohol converts the lithiated betaine 104B into threo-103, which collapses upon treatment with potassium tert-butoxide or heating to the corresponding E-alkene 105 with selectivities typically greater than 98:1 (Scheme 36).

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