19952-66-0Relevant articles and documents
Enantioselective Cyclopropanation of 4-Nitroisoxazole Derivatives
Do?ekal, Vojtěch,Petr?elová, Simona,Císa?ová, Ivana,Vesely, Jan
supporting information, p. 2597 - 2603 (2020/04/30)
The present study reports an asymmetric organocatalytic cascade reaction of 4-nitroisoxazole derivative with α,β-unsaturated aldehydes catalysed by chiral secondary amine. Using this approach, 1,2,3-trisubstituted cyclopropane products were obtained in isolated yields up to 98% with moderate diastereoselectivities, and enantiopurity up to 99% ee. Moreover, this synthetic protocol can be used for further applications, as shown by a set of additional transformations of the corresponding cyclopropanes and by the formal synthesis of GABA ligands. (Figure presented.).
Cyclopropanediamines, 3. - Pure Diastereomers of 1,2-Cyclopropanedicarboxylic Acids and Derivatives
Saal, Wolfgang von der,Reinhardt, Robert,Seidenspinner, Hubert-Matthias,Stawitz, Josef,Quast, Helmut
, p. 703 - 712 (2007/10/02)
Efficient preparations of pure diastereomers of dimethyl 1,2-cyclopropanedicarboxylates 2, dicarboxylic acids 3, dicarbonyl dichlorides 4, and dihydrazides 5 are reported.Mixtures of diastereomers of dimethyl dicarboxylates 2a, b, d, e are obtained from α,β-unsaturated methyl carboxylates 7 and methyl α-chlorocarboxylates 8 as well as from 7c, d and the sulfur ylide 10 (2c, d).The diastereomers are separated by fractionating distillations (2a, b, c, e) or crystallization (2d) on a 100-g to 1-kg scale (d.e. >99percent).Only low yields of 2c are obtained in the reaction of methyl crotonate (7c) with methyl α-chloroacetate (8a), since 7c predominantly dimerizes to afford 12.The diesters 2 are converted into the pure diastereomeric diacids 3, dicarbonyl dichlorides 4, and dihydrazides 5. 3,3-Dimethyl-cis-1,2-cyclopropanedicarboxylic acid (cis-3f) is obtained by trans-->cis isomerization of trans-3f with the help of acetic anhydride and sodium acetate as catalyst.The configurations of 2-6 and 12 are confirmed by 1H NMR spectroscopy.Derivatives of cis-1,2-dimethyl-1,2-cyclopropanedicarboxylic acid tend to form bicyclic products.Thus, the reaction of cis-3e with phosphorus pentachloride yields mainly the cyclic anhydride 6e and only small amounts of the dicarbonyl dichloride cis-4e.Furthermore, the dihydrazide cis-5e slowly cyclizes in the solid state to give the N-aminoimide 13 and hydrazine, a reaction which is fast in solution.Pure 13 is obtained by thermolysis of cis-5e at 60-65 deg C under high vacuum.
