Stereoselective synthesis of (<i style="">2R</i>, <i style="">3S</i>, <i style="">22R</i>, <i style="">23E</i>)-6, 6-ethylenedioxy-22-hydroxy- 2, 3- isopropylidenedioxy-24-methyl-5<img src='/image/spc_char/alpha.gif' border=0>-cholest-23-ene: An intermediate for the synthesis of castasterone, dolichosterone and brassinolide

Abstract

Wittig reaction on (<i style="">2R</i>, <i style="">3S</i>)-2,3-isopropylidenedioxy-6,6-ethylene-dioxy-5<img src='/image/spc_char/alpha.gif' border=0> -pregnane-(<i style="">20S</i>)-20-carbaldehyde<b style=""> 6</b>,<b style=""> </b>furnishes stereoselcctively an <i style="">22</i>(<i style="">E</i>)-<img src='/image/spc_char/alpha.gif' border=0> ,<img src='/image/spc_char/beta.gif' border=0>-unsaturated ketone <b style="">7</b>, which on reaction with methyllithium followed by 1,3-carbonyl trans­position and stereoselective reduction with DIBAL-H affords the title compound<b style=""> 10</b>, an intermediate for castasterone, dolicho­sterone and brassinolide.