Since they don't need to be isolated during their most famous application, they are produced in situ using such deprotonating agents as NaHMDS.
One of these compounds formed from a deprotonated thiazolium salt can replace cyanide as a catalyst in a reaction which adds aldehydes to a,?-unsaturated compounds. One of these compounds formed from carbon tetrabromide reacts to form a dibromoalkene intermediate before reacting with butyllithium to form an alkyne from an aldehyde. In addition to being used in the Stetter reation, they are also used in a reaction which produces cyclopropanes from enones and (*) epoxides from ketones. Since they don't need to be isolated during their most famous application, they are produced in situ using such deprotonating agents as NaHMDS. In that scheme, one of these reacts with a carbonyl to form a 4-membered ring which opens to produce a (Z)-alkene. For 10 points, name this functional group in which adjacent atoms feature positive and negative charges, exemplified by a sulfonium variety used in the Corey-Chaikovsky reaction and a phosphonium variety used in the Corey-Fuchs and Wittig Reactions.
One of these compounds formed from a deprotonated thiazolium salt can replace cyanide as a catalyst in a reaction which adds aldehydes to a,?-unsaturated compounds.
{ylide} [prompt on {zwitterion}]