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 ester or unstabilized (10[1])alkyl reagents. Maryanoff and Reitz coined the term “stereochemical drift” to describe the interconversion of betaine intermediates in this reaction, (10[1])which can be controlled using the Schlosser modification. (10[1])A modification of this reaction that uses carbanion reagents to preferentially synthesize E products was proposed by Leopold Horner. In lithium-free conditions, this reaction proceeds via a four-atom oxaphosphetane intermediate. For 10 points, name this reaction that uses a triphenyl phosphonium ylide (“ILL-id”) reagent to convert a carbonyl group into an alkene. ■END■ (0[2])