کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5274579 | 1385514 | 2009 | 4 صفحه PDF | دانلود رایگان |
cis-Chrysanthemic acid has been prepared in a few steps from dimethyldimedone via dibromination at alpha positions of each carbonyl carbons. The trans-dibromide which is almost exclusively formed has been isomerized to its cis-stereoisomer by highly chemoselective tandem H/K-K/H exchanges involving potassium bases at low temperature (<â40 °C). Carbocyclization of the potassium enolate intermediate takes place at around â30 °C and provide the bicyclo[3.1.0]-hexane skeleton. Lithiated bases behave differently and mainly lead to Br/M rather than to H/M exchange. We have been unsuccessful in using state of the art enantioselective metallation reactions to achieve the enantioselective synthesis of (1R)-cis-chrysanthemic acid using the disclosed strategy. This therefore still remains challenge.
Journal: Tetrahedron Letters - Volume 50, Issue 20, 20 May 2009, Pages 2398-2401