Diastereoselective Darzens condensations

Effect of Phase-Transfer Catalyst on Stereochemistry oftert-Butyl-3-aryl(alkyl)-Substituted Glycidates

“…A PT-catalyzed process afforded mainly the trans -2,3-diphenylglycidonitrile, while the uncatalyzed reaction led to both diastereoisomers in comparable amounts . Neither this explanation nor the results of a diastereoselective Darzen’s condensation of N , N -diphenyl-α-haloacetamides with aromatic aldehydes satisfactorily explain our results, however. While we would have preferred a better mechanistic understanding of these results, the chemistry is useful for certain substitution patterns and suggests high diastereomeric ratios in the Darzen’s reaction are possible by varying the substitutents.…”

A Novel Diastereoselective Synthesis of 6‐Aryl‐5‐hydroxy‐2,3‐dihydropyrano[2,3‐c]pyrazol‐4(1H)‐ones

“…Epoxides are particularly versatile synthetic intermediates that can readily be converted into a wide range of polyfunctional compounds. A useful method for the synthesis of α,β‐epoxy‐carbonyl compounds is the Darzens condensation between a carbonyl compound and an α‐halo‐carbonyl compound . The presence of a hydroxyl group at C‐2′ makes the α,β‐epoxy‐carbonyl compounds difficult to isolate as they undergo a cyclization to give dihydroflavonols formed by attack upon the β‐carbon of the epoxides .…”