Phase-transfer-catalyzed asymmetric glycolate alkylation.
[reaction: see text] Asymmetric surrogate glycolate alkylation has been performed under phase-transfer conditions. Diphenylmethyloxy-2,5-dimethoxyacetophenone with trifluorobenzyl cinchonidinium catalyst and cesium hydroxide provided alkylation products at -35 degrees C in high yield (80-99%) and with excellent enantioselectivities (90:10 to 95:5). Useful alpha-hydroxy products were obtained using bis-TMS peroxide Baeyer-Villiger conditions and selective transesterification. The intermediate aryl ester can be obtained with >99% ee after a single recrystallization. A tight ion-pair model for the observed (S)-stereoinduction is proposed.
Andrus
Merritt B
MB
Brigham Young University, Department of Chemistry and Biochemistry, C100 BNSN, Provo, Utah 84602-5700, USA. mbandrus@chem.byu.edu
Hicken
Erik J
EJ
Stephens
Jeffrey C
JC
D000098:Acetophenones; D000478:Alkylation; D001593:Benzyl Compounds; D002384:Catalysis; D002930:Cinchona Alkaloids; D006016:Glycolates / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
D000098:Acetophenones; D001593:Benzyl Compounds; D002930:Cinchona Alkaloids; D006016:Glycolates; C041622:cinchonidine