Hydroxynitrile lyase catalyzed enantioselective HCN addition to O-protected α-hydroxyaldehydes
作者:Jürgen Roos、Franz Effenberger
DOI:10.1016/s0957-4166(99)00275-x
日期:1999.7
Various O-protected glycol- and racemic lactaldehydes 3 and 6 as well as O-allyl protected racemic alpha-hydroxyaldehydes 7 (R-1=Et Pr, Bu) have been prepared to investigate and perform a stereoselective Kiliani-Fischer synthesis by hydroxynitrile lyase (HNL) catalyzed addition of HCN. From all protecting groups investigated the allyl moiety was most suitable. (R)-PaHNL from bitter almonds (Prunus amygdalus), yielding the (2S)-cyanohydrins 8-10, was found to be a more stereoselective catalyst than (S)-MeHNL from maniok (Manihot esculenta). While (R)-PaHNL led to enantiomeric excesses greater than or equal to 93%, with (S)-MeHNL the (2R)-cyanohydrins 8-10 were obtained with enantiomeric excesses less than or equal to 78%. (C) 1999 Elsevier Science Ltd. All rights reserved.
CeCl<sub>3</sub>·7H<sub>2</sub>O−NaI Catalyzed Hydrooxacyclization of Unsaturated 3-Hydroxy Esters
[GRAPHICS]Cerium(III) chloride heptahydrate and sodium iodide in boiling acetonitrile promote cyclization of 3-hydroxyalkenoic acids esters giving 5-substituted tetrahydrofuranacetic acid esters and 6-substituted tetrahydropyranacetic acid esters in fair to good yield and with complete retention of the absolute configuration of the starting 3-hydroxy ester.
Intramolecular Chirality Transfer [2 + 2] Cycloadditions of Allenoates and Alkenes
作者:Yao Xu、Young J. Hong、Dean J. Tantillo、M. Kevin Brown
DOI:10.1021/acs.orglett.7b01420
日期:2017.7.21
Intramolecular chirality transfer [2 + 2] cycloaddition of enantiomerically enriched allenoates and alkenes is presented. The use of a chiral catalyst was found to be critical to achieve high levels of diastereoselectivity compared to use of an achiral catalyst. The method developed leads to highly substituted cyclobutanes that would be difficult to prepare by alternative methods.