Synthesis and Characterization of Chiral Guanidines und Guanidinium Salts Derived from 1-Phenylethylamine

Chelating P2‐Bis‐phosphazenes with a (R,R)‐1,2‐Diaminocyclohexane Skeleton: Two New Chiral Superbases

“…[21b] Racemizationduring PÀNbond formation could be excluded on the basis of the absolute configurationr evealedb yX RD analyses. Flack parameters of À0.02 (7), À0.08 (9), and 0.02(1), respectively,w ere found for the crystal structures in We did not obtain single crystalso famonoprotonateds pecies suitablef or XRD analysis to obtain experimental evidence for the theoretically predicted bis-equatorial conformation in solution and in the gas phase.…”

“…In this context, chiral guanidines play a key role, as reviewed by the groups of Ishikawa and Leow . This compound class exhibits great structural variety, as reflected by species such as C 3 ‐symmetric guanidinium salts discussed by Kantlehner or chelating axial chiral species reported by Himmel et al . Diels–Alder reactions, Michael additions, Henry reactions, or nucleophilic epoxidations are only a few examples of asymmetric transformations catalyzed by chiral guanidines.…”

“…In this context,c hiral guanidines play ak ey role, as reviewed by the groups of Ishikawa and Leow. [6] This compound class exhibits great structural variety, as reflected by species such as C 3 -symmetric guanidiniums alts discussed by Kantlehner [7] or chelating axial chiral speciesr eported by Himmel et al [8] Diels-Alder reactions, [9] Michael additions, [10] Henry reactions, [11] or nucleophilic epoxidations [12] are only af ew examples of asymmetric transformationsc atalyzed by chiral guanidines.H owever,d ue to the relatively low basicity of classical representatives of this compound class-achiral pentamethyl guanidine only reveals ap K BH + value of 25.0 [13] in acetonitrile-their scopei nB rønsted base catalysis is limited to comparably acidic substrates.C onsiderablec urrent interest in chiral superbases with pK BH + values beyond those of ordinary guanidines becomes evident when regardingt he high-ranking publications in this field in recent years:t hree works on chiral cyclopropenimines as catalysts for Michaela dditions and Mannichr eactions were published by the group of Lambert since 2012. [14] Ta keda and Te rada presented as eries of chiral bis(guanidino)iminophosphoranes in 2013.…”

Synthesis, Characterization and Antibacterial Activity of Novel 1,3-Diethyl-1,3-bis(4-nitrophenyl)urea and Its Metal(II) Complexes

“…The ligand was prepared according to the previous literature with slight modification [23]. In a 250 mL clean two-necked round-bottomed flask, containing an ice-cooled mixture of N -ethyl-4-nitroaniline (16.6 g, 0.1 mol) in dichloromethane (100 mL), a solution of phosgene in toluene (20%, 25 mL, 0.05 mol) was slowly introduced over a period of 30 min.…”

New Advances in the Synthetic Application of Enantiomeric 1-Phenylethylamine (α-PEA): Privileged Chiral Inducer and Auxiliary

“…Guanidines and guanidinium salts are often used in organic synthesis (strong bases, catalysts, or ionic liquids) and also constitute a part of natural compounds (L-arginine, polycyclic marine alkaloids). Jäger and coworkers described the new efficient synthesis of chiral guanidines and guanidinium salts based on optically active α-PEA ( Scheme 42 ) [ 65 ]. Unfortunately, the attempted catalytic use of the obtained guanidine and guanidinium iodide in asymmetric transformations (Morita–Baylis–Hillman, Michael, and epoxidation reactions) did not result in a noteworthy stereoinduction [ 65 ].…”