Asymmetric trimethylsilylcyanation of benzaldehyde catalyzed by (salen)Ti(IV) complexes derived from (R)- and/or (S)-4-hydroxy-5-formyl[2.2]paracyclophane and diamines

Synthesis, characterization and catalytic property of tetradentate Schiff-base complexes for the epoxidation of styrene

“…The peaks at 6.779-7.285 ppm are attributed to aromatic protons ( C H), and those at 1.477-1.754 ppm, 1.903 (cis) and 1.971 ppm (trans) to the protons of CH 2 in the ring of cyclohexane. Two proton peaks at 8.254 (cis) and 8.315 (trans) ppm can be assigned to CH N protons, consistent with the observations made by Belokon et al [30], who had assigned H NMR peaks of 2H at 8.2-8.4 ppm in the salen compounds to CH N protons. In a similar manner to Schiff-base ligand L 1 , the H NMR peak at 10.102 ppm For Schiff-base ligand L 3 , twin H NMR peaks at 14.659 (cis) ppm and 14.793 (trans) ppm can be attributed to naphtholic OH protons.…”

Enantioselektive Strecker‐Reaktion mit einem Organokatalysator ohne Wasserstoffbrückendonor‐Funktion

“…[7] Wir beschreiben hier einen neuen Typ von Organokatalysatoren für die enantioselektive Strecker-Reaktion, dessen Bauelemente Glycosylamine [8] und planar-chirale [2.2]Paracyclophan-Derivate sind. Chirale [2.2]Paracyclophane [9] wurden bereits in der enantioselektiven Synthese verwendet, wie etwa Titan-Komplexe von salenartigen Derivaten des [2.2]Paracyclophans [10] in der enantioselektiven CyanhydrinBildung aus aromatischen Aldehyden [11] oder in enantioselektiven Additionen von Zinkdiethyl an Aldehyde.[12] Der Versuch, [2.2]Paracyclophan-4-carbaldehyd (2) [13] (Schema 1) durch Iminbildung mit 2,3,4,6-Tetra-O-pivaloyl-b-d-galactopyranosylamin 1 [8a,b] einer kinetischen Racematspaltung zu unterwerfen, war nicht erfolgreich. Die diastereomeren Imine ließen sich aber trennen, sodass das Imin 3 als reines (b-d,R)-Stereoisomer erhalten wurde.…”

Enantioselective trimethylsilylcyanation of benzaldehyde using pyrrolidine-based chiral salen ligands

“…The greater selectivities observed in the presence of these ligands is in agreement with our previous studies and with those of others which demonstrate that bulky groups in C3 and C3' and/or in C5 and C5' of the aldehyde moieties of salen ligands are fundamental characteristics for high selectivity. [7][8][9][10][11][12][23][24][25] The rigid cyclic backbone structure of the 1,2-diamine is probably also responsible for these selectivities. We have previously observed that, with the same aldehyde moieties but with less rigid backbone structures of 1,3-diamines derived from camphoric acid, lower selectivities are obtained.…”