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.