stereoselectivity of the Horner–Wadsworth–Emmons reaction of ketones is poor to modest. Variations Base sensitive substrates Since many substrates are not stable to sodium hydride, several procedures have been developed using milder bases. Masamune and Roush have developed mild conditions using lithium chloride and DBU. Rathke extended this to lithium or magnesium halides with triethylamine. Several other bases have been found effective. Still modification W. Clark Still and C. Gennari have developed conditions that give Z-alkenes with excellent stereoselectivity. Using phosphonates with electron-withdrawing groups (trifluoroethyl) together with strongly dissociating conditions (KHMDS and 18-crown-6 in THF) nearly exclusive Z-alkene production can be achieved. Ando has suggested that the use of electron-deficient phosphonates accelerates the elimination of the oxaphosphetane intermediates. See also Wittig reaction Michaelis–Arbuzov reaction Michaelis–Becker reaction Peterson reaction Tebbe olefination References Olefination reactions Carbon-carbon bond forming reactions Name reactions