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DOI: 10.1055/sos-SD-027-00002

Aggarwal, V.; Richardson, J.Science of Synthesis, (20042760.

The most common approach to the generation of sulfonium ylides by deprotonation is to add an appropriate base to a solution of the preformed sulfonium salt. A wide range of ylides are synthesized by this method. Those that cannot be isolated are commonly trapped in situ, generally with carbonyl compounds to give epoxides (see Section The choice of solvent for the reaction strongly depends on a number of factors, such as the stability of the ylide, the freezing point of the solvent, the solubility of the sulfonium salt in the solvent, and the intended application of the ylide. Alcohol solvents, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, or dichloromethane are commonly used for such deprotonation reactions. The solubility of sulfonium salts in ether solvents is strongly dependent on the counterion and generally increases in the order iodide < bromide < chloride < tetrafluoroborate.[‌3‌] Sulfonium halides are readily converted into sulfonium tetrafluoroborates by anion metathesis using silver tetrafluoroborate or sodium tetrafluoroborate in acetone.[‌185‌] A wide variety of bases is employed for the deprotonation of sulfonium salts: alkyllithiums (typically in THF, although sometimes in Et2O, HMPA, or MeCN), amide bases such as lithium diisopropylamide or lithium, sodium, or potassium hexamethyldisilazanide (typically in THF; however, formation of 100 in Scheme 53 is achieved in DME), secondary and tertiary amines, sodium hydride (typically in THF or DMSO, see the formation of 101 in Scheme 53), alkoxide bases (typically in alcohol solvents, DMSO, THF, or toluene), and metal hydroxides (typically in water or alcohol solvents).

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