Regioselective and Stereoselective Nucleophilic Ring Opening of Trifluoromethylated Cyclic Sulfates: Asymmetric Synthesis of Both Enantiomers of <i>s</i><i>yn</i>-(3-Trifluoromethyl)isoserine
作者:Zhong-Xing Jiang、Feng-Ling Qing
DOI:10.1021/jo0497611
日期:2004.8.1
novel and efficient enantioselective synthesis of both enantiomers of syn-(3-trifluoromethyl)isoserine was achieved. Ring opening of trifluoromethylated cyclic sulfates 3, derived from enantiopure trifluoromethylated vicinal diols 2, with various nucleophiles occurred exclusively at C2 with inversion of chirality. Treatment of 4c and 4d, obtained by nucleophilic opening of 3a and 3b with PhCO2NH4, with
Trifluoromethylated analogs of macrosphelide A I and 2 were designed and synthesized. The key segment 6 was efficiently constructed via a series of high stereoselective transformations from trifluoromethylated diol 8. Methoxymethylation of compound 9 with 14 1.0 equiv of sodium hydride gave optically pure compound 23a in 73% yield. From 23a a novel route was developed to prepare key segment 7. The condensation and macrolactonization were smoothly proceeded under our modified Keck's protocol. (c) 2007 Elsevier Ltd. All rights reserved.
Synthesis of trifluoromethylated analogues of β-l-fucofuranose and β-l-4,6-dideoxyxylohexopyranose
Efficient strategy to trifluoromethylated trans-disubstituted alkene 3 was developed starting from commercially available 4,4,4-trifluoro-3-oxobutyric acid ethyl ester 12. 6-Deoxy-6,6,6-trifluorosugars 21 and 30 were synthesized from 3 in high stereoselectivity and in a straightforward fashion. The key steps were Sharpless AD reaction, regioselective ring opening of trifluoromethylated cyclic sulfate, Horner-Wadsworth-Emmons reaction and TEMPO oxidation. It was noteworthy that the oxidation of alcohols 20 and 29 followed by deprotection and acetylation gave the single isomer target molecules 21 and 30, respectively. (C) 2005 Elsevier B.V. All rights reserved.