This reaction is the basis for a modification that uses electron-deficient reagents in a mixture of KHMDS and 18-crown-6. Semi-stabilized aryl reagents in this reaction do not achieve stereoselectivity, unlike stabilized (10[1])ester or unstabilized alkyl reagents. Maryanoff and Reitz coined the term “stereochemical drift” to describe the interconversion of betaine intermediates in this reaction, which can be controlled using the Schlosser modification. A modification of this reaction that uses carbanion reagents (10[1])to preferentially synthesize E products was proposed by Leopold Horner. In lithium-free conditions, this reaction proceeds via a four-atom (10[1])oxaphosphetane intermediate. For 10 points, name this reaction that uses a triphenyl phosphonium ylide (“ILL-id”) reagent (10[1])to convert a carbonyl group into an alkene. ■END■