Enantioselective synthesis of chiral caronic esters : application to the syntheses of (1)-trans-chrysanthemic acid and its (1)-cis-dibromo vinyl analogue from dimethyl fumarates

Diastereoselective Additions to C,C Double Bonds Applied to the Enantioselective Synthesis of Pyrethroic Acids

“…Lactonization of methyl trans-3-(1,2-dihydroxy-ethyl)-2,2-dimethyl-cyclopropanecarboxylate which requires a contrathermodynamic trans/cis isomerisation to deliver 4hydroxymethyl-6,6-dimethyl-3-oxa-bicyclo[3.1.0]hexan-2one was not as obvious as we expected since at the contrary of methyl trans-3-hydroxymethyl-2,2-dimethyl-cyclopropanecarboxylate which misses extra hydroxymethylene group [10], it was insensitive to potassium t-butoxide.…”

“…Nevertheless, significant improvement were made using isopropylidenetriphenylphosphorane and either di(l)-menthyl fumarate (THF, -78 to +20 °C, 85 %, (S,S) de: 74 %, Scheme 5, entry a) [10] or di(l)-phenyl-menthyl fumarate (THF, -78 to +20 °C, 80 %, (S,S) de: 82 %, Scheme 5, entry b) [10].…”

“…Using isopropylidenediphenylsulfurane instead, gave poorer asymmetric induction (THF, -78 to + 20 °C, 79 %, (S,S) de 22 %, Scheme 5, entry c) [10]. Asymmetric induction has been suggested to occur from the carboxy group on the fumarates adjacent to the site which is attacked by the ylide.…”

Monoterpenoids

“…Elimination of acetic acid from (191) (by heating it, in decalin) yields a mixture of isomeric terpinyl acetates. 23 The terpinen-4-01 (192) is stereoselectively hydrogenated to (193) in the presence of [Ir(cod)(P(C,H, 1)3}(py)]PF6, due to chelation of its hydroxyl group to the catalyst.232 cis-Carveol (159) gives the inverted chloride (194), together with pinol (195), if it is refluxed with PPh3 in carbon t e t r a ~h l o r i d e . ~~~ The pivalate (196) couples with BuLi, in the presence of CuI, to yield (197)234 (cf: ref 138).…”

Zweistufige Synthese vontrans-2-Arylcyclopropancarbonsäureestern in 98–100 %ee mit Hilfe einer Phosphazenbase

“…[6,7] Daher könnte die Schwefel-Ylid-Methode, wie bereits Corey feststellte, [8] für die Synthese in gröûerem Maûstab geeigneter sein. Bisher muûte dabei jedoch ein chirales Olefin als Edukt eingesetzt werden, und entweder die Ausbeuten [9] oder der Diastereomerenüberschuû [10] war gering. In der hier beschriebenen Methode befindet sich die Chiralität im schwefelhaltigen Reagens, das zurückgewonnen und deshalb wiederverwendet werden kann (Schema 1 Ausgehend von RCH 2 OH, Tf 2 O und Pyridin oder RCH 2 Br und AgBF 4 in CH 2 Cl 2 wurden die Arylmethylsulfoniumsalze 2 a ± d in 80 ± 85 % Ausbeute hergestellt.…”