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231.
The cyclic [2R,S(R)]‐bornane‐10,2‐sulfinamide (−)‐ 2b , an analogue of Oppolzer`s camphor‐derived sultam (−)‐ 2a , was synthesized by reduction of the known N‐alkylidenesulfinamide (+)‐ 1b with NaBH4. The uncatalyzed [4+2] cycloaddition of cyclopentadiene to the methyl ester (−)‐ 3b of the N‐fumaroylsulfinamide, obtained from (−)‐ 2b , proceeds with lower endo and π‐facial selectivity as compared to dienophiles (−)‐ 3a , c . In contrast to these latter, the diastereoselectivity is reversed either in apolar CCl4 or in the presence of TiCl4. This inversion is explained by a competitive C(α)‐si addition on the reactive anti‐s‐trans conformer. 相似文献
232.
Jaroslaw Kiegiel Christian Chapuis Zofia Urbaczyk-Lipkowska Janusz Jurczak 《Helvetica chimica acta》1998,81(9):1672-1680
Cycloadditions of 1-methoxybuta-1,3-diene to (2R)-N-pyruvoyl and (2R)-N-(phenylglyoxyloyl)bornane-10,2-sultam ((−)- 1b and (−)- 1c , resp.) under high-pressure conditions are presented. The absolute configurations of the cycloadducts 2b,c and of their resulting reduced alcohols 3b,c are based on their X-ray analyses. The stereochemical course of these reactions is discussed and compared to the inverse diastereoselectivity observed for the analogous cycloaddition to (2R)-N-glyoxyloylbornane-10,2-sultam ( 1a ) 相似文献
233.
Jadwiga Frelek Irma Panfil Agata Klimek Zofia Urbaczyk‐Lipkowska Marek Chmielewski 《Helvetica chimica acta》2002,85(7):2138-2148
The relationship between chiroptical properties of substituted bicyclic isoxazolidin‐5‐one derivatives and their molecular structures was investigated. The chromophoric system in isoxazolidinones was found to be nonplanar with a shallow pyramidal configuration at the N‐atom. The deviation from planarity can be attributed to the strain imposed by the bicyclic skeleton. Due to the nonplanarity, the isoxazolidinone system becomes inherently dissymmetric, which is supported by the high magnitude of the CD band occurring around 210 nm. In addition, the helicity of lactone moiety in investigated bicyclic isoxazolidinones is controlled by the absolute configuration at C(6). On this basis, a helicity rule correlating a positive (negative) helicity expressed by the OC(8) O(9) N(1) torsional angle with a positive (negative) sign of the CD band around 210 nm was formulated. 相似文献
234.
Daniel Taton Agnieszka‐Zofia Wilczewska Mathias Destarac 《Macromolecular rapid communications》2001,22(18):1497-1503
Double hydrophilic statistical, diblock and triblock copolymers comprised of acrylamide and acrylic acid units have been synthesized in aqueous medium using the MADIX process. Starting from an either monofunctional or difunctional xanthate, the resulting AB and ABA‐type double hydrophilic block copolymers (DHBC) exhibited molar masses predetermined by the initial monomer/xanthate precursor molar ratio and polydispersity indices in the range 1.2–1.5. Batch copolymerizations yielded well‐defined statistical copolymers that were chain‐extended for the synthesis of novel poly‐ (acrylic acid‐stat‐acrylamide)‐block‐polyacrylamide DHBC. 相似文献