Precursor of Wittig ylide for methylenation of carbonyl compounds. See, e.g.: Org. Synth. Coll., 5, 751 (1973). A simplified procedure using K2CO3 in triglyme has been reported: Synth. Commun., 22, 513 (1992).
Where the ylide is insufficiently reactive, a further proton can be removed by s-BuLi or t-BuLi, and the resulting lithio ylide reacted with hindered ketones such as fenchone: J. Am. Chem. Soc., 104, 4724 (1982).