Enantio- and diastereocontrolled conversion of chiral epoxides to trans-cyclopropane carboxylates: application to the synthesis of cascarillic acid, grenadamide and <scp>l</scp>-(−)-CCG-II
作者:Pradeep Kumar、Abhishek Dubey、Anand Harbindu
DOI:10.1039/c2ob25622c
日期:——
An efficient high yielding improved method for the enantio- and diastereoselective cyclopropanation of chiral epoxides using triethylphosphonoacetate and base (Wadsworth–Emmons cyclopropanation) is reported. The utility of this protocol is illustrated by concise and practical synthesis of cascarillic acid, grenadamide and L-(−)-CCG-II, a cyclopropane containing natural products.
Optionally isolated and/or purified enatiomers of 2-heptylcyclopropyl-1-carboxylic acid and mixtures of two, three or all enantiomers of 2-heptylcyclopropyl-1-carboxylic acid are disclosed as perfumes and/or flavourings.
The cyclopropane ring in 2-substituted 1, 1-cyclopropanedicarboxylates was regioselectively opened by using samarium(II) diiodide (SmI2) in a hexamethylphosphoric triamide (HMPA)-tetrahydrofuran (THF) (1 : 10) system under mild and neutral conditions to give (2-substituted ethyl)malonates in moderate to good yields. The cyclopropane ring in 2-substituted cyclopropanecarboxylates or 2-substituted 3-(trimethylsilyl)cyclopropanecarboxylates was similarly cleaved regioselectively by using SmI2 in a HMPA-THF (1 : 1) system to give 4-arylbutyrates or 4-aryl-3-(trimethylsilyl)butyrates in 16-89% yields. The reaction mechanism of these ring-opening reactions is discussed.
Offenbart werden gegebenenfalls isolierte und/oder aufgereinigte Enantiomere der 2-Heptylcyclopropyl-1-carbonsäure sowie Gemische von zwei, drei oder sämtlichen Enantiomeren der 2-Heptylcyclopropyl-1 carbonsäure als Duft-und/oder Aromastoffe.