I. Izquierdo, M. T. Plaza, Miguel A. Rodríguez
Feb 19, 2001
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Journal
Tetrahedron-asymmetry
Abstract
Abstract ( R,S )-1,3-Butanediol 5 was kinetically resolved by enzymatic acetylation with vinyl acetate under the presence of Chirazyme™ L -2, c–f, yielding ( S )-1- O -acetyl-1,3-hydroxybutane 6 and ( R )-1,3-di- O -acetyl-1,3-butanediol 7 with enantiomeric excesses of 91% ( E =67.3). Compounds 6 and 7 were easily transformed into the corresponding ( S )-3- O -(2-methoxyethoxymethyl)-3-hydroxybutanal 10 and ( R )-3-benzyloxybutanal 19 , through a protection–deprotection and functional group interchange methodology. Subsequent reaction of 10 and 19 with 3-(methoxycarbonylpropionylmethylene)triphenylphosphorane afforded methyl ( E , S )-8- O -(2-methoxyethoxymethyl)-4-oxo-5-nonenoate 12 and ( E , R )-8-benzyloxy-4-oxo-5-nonenoate 20 . The alkenes 19 and 20 were then catalytically hydrogenated to the corresponding saturated esters 13 and 21 . Treatment of 13 and 21 with 1,2-ethanedithiol/F 3 B·OEt 2 afforded dithioketals 14 and 22 , which were respectively reduced to ( S )-1,8-dihydroxy-4-nonanone ethylidenedithioketal 15 and ( R )-8- O -benzyl-1,8-dihydroxy-4-nonanone ethylidenedithioketal 23 . Finally, deprotection of 15 by catalytic hydrogenation under acidic conditions gave the expected (5 S ,7 S )-(−)-7-methyl-1,6-dioxaspiro[4.5]decane 1 . The (5 R ,7 R )-(+)- 1 enantiomer was analogously prepared from 23 . Both compounds were formed by this procedure with an e.e. of 91%.