The highly trans-selective Darzens reaction via ammonium ylides

The Darzens reaction using electron deficient p-substituted benzyltriethylammonium chlorides with aromatic aldehydes afforded 2,3-diaryl epoxides with trans selectivity (> 99%) while the corresponding reaction with electron releasing p-substituted benzyltriethylammonium salts gave the epoxides as diastereomeric mixtures. Epoxide formation of p-trifluoromethylbenzylammonium salt, prepared from p-trifluoromethylbenzyl chloride and DABCO, afforded the corresponding 2,3-diaryl epoxide in high yield (> 98%).