Bases Schilf

Finally, Sinou el al. have employed a chiral tetrasulfonated diphosphine as a ligand in the Rh-catalysed reduction of the Schilf base depicted in Scheme 8.34. In the presence of an aqueous-organic two-phase solvent system, a quantitative yield combined with a moderate enantioselectivity of 34% ee were obtained for this reaction. 

Hayashi et al.147 reported another highly enantioselective cyanohydrination catalyzed by compound 138. In this reaction, a Schilf base derived from fl-amino alcohol and a substituted salicylic aldehyde were used as the chiral ligand, and the asymmetric addition of trimethylsilylcyanide to aldehyde gave the corresponding cyanohydrin with up to 91% ee (Scheme 2-56). 

Anodic oxidation of o-amino substituted aromatic Schilf bases (38 and 40) to imidazole derivatives 39 and 41 were carried out in CH3CN-O.I mol/1 Et4C104 solution with addition of pyridine as a base, using controlled potential electrolysis and a divided cell [72] (Scheme 22). 

The importance of metal coordination compounds in biological systems has led to the study of polydentate Schilf base complexes of cobalt(II), nickel(II), and copper(II) (204, 205). Dimers have been observed in the spectra of complexes of both tri- and tetradentate ligands [e.g., salicylaldehydeand A,A-bis(salicylidene)ethylenediamine]. The parent ions form the base peaks, and the spectra are characterized... 

On the other hand, Eichhorn (27, 57) has shown that the Schilf base of salicylaldehyde with glycine is stabilized by chelate formation at pH values where the free ligand is readily hydrolyzed. 

NMR studies have been mainly applied to elucidating the structural features of Schilf bases in solution. These studies are mainly concerned with SchiiT bases derived from benzaldehyde and its substituents, / -diketones, o-hydroxyacetophenones and o-hydroxyacetonaphthones. They were devoted to obtaining an insight into the keto-enol equilibrium (Scheme 1), syn and anti isomerism and steric distortions in different kinds of solvents. Relevant data and results are described in the following sections. 

The reactions of several Co(n) complexes have been examined (Halpern, 1974), namely, pentacyanocobaltate(n) (Chock and Halpern, 1969 Halpern and Maher, 1964,1965 Kwiatek and Seyler, 1965,1968 Kwiatek, 1967), bis-(glyoximato)cobalt(n) (Schneider et at., 1969), cobalt(n) Schiff s base (Marzilli et at., 1970, 1971) and bis(dioximato)cobalt(n) (Halpern and Phelan, 1972) complexes. A halogen-atom-transfer mechanism has been proposed for most halides (158, 159), with the exception of the reaction of cobalt(n) Schilf s... 

Asp-96, a key residue in the middle of the relatively hydrophobic cytoplasmic half-channel about 11 A from the protonated Schilf base, is protonated in the ground state. Its only polar interaction stems from a hydrogen bond to the hydroxyl of Thr-46. Otherwise it is surrounded by a hydrophobic barrel whose walls are formed by residues IleA5, Leu-223, and Leu-224, and the lids by Phe-42, Leu-99, and Leu-100 on the cytoplasmic side, and by Val-49, Leu-93, and Phe-219 Schiff base side. In the M to N transition of the photocycle, reprotonation of the Schiffbase from Asp-96 can occur only after this hydrophobic region between the Schiffbase and Asp-96 has been populated by a chain of water molecules (Luecke et al., 2000b). 

A similar treatment of the Schilf s base derived from 3-nitro-2-thienylcarbaldehyde (564) with triethyl phosphite gave the thieno[3,2-h]pyrazole (565) (78CC453). ... 

Treatment of an aldehyde or ketone with a 1 amine affords an imine (also called a Schilf base). Nucleophilic attack of the 1° amine on the caibonyl group forms an unstable carbinolamine, which loses water to form an imine. The overall reaction results in replacement of C=O by C=NR. 

Schilf base (Section 21.11 A) A compound having the general structure R2C=NR. ASchiff base is also called an imine. 

The photodecarboxylation of alkoxyacetic acids in the presence of HgO and iodine has been studied.Karauchi et al. have studied the photodecarboxylation of the Schilf base (117). Low-temperature matrix isolation techniques have been used to trap and study the pyranone (118) obtained by the decarboxylation of the dilactone (119). Photodecarboxylation of the carbamates (120) in acetonitrile provides a simple route to the azabicyclobutanes (121). ... 

Organic compounds bearing heteroatoms from the same column in the periodic table also react by similar paths. Photocatalytic oxidation of primary amines on irradiated semiconductor suspensions, for example, forms Schilf bases which can couple with the starting amine [124]. Two different products are formed, depending on the initial concentration of the amine and on the nature of the semiconductor catalyst (Eq. 15) [125]. 

Figure 36. Schilf base ligands that have been covalently bound to MCM-41 framework.

Further extension of the reaction pool of Schilf bases 138 was achieved by their reaction with tran -l-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky s diene) to give 2-substituted 5,6-didehydro-piperidin-4-ones 164 [135,136] (Scheme 10.54). The reaction is considered to be a sequence of an initial Mannich reaction between the imine and the silyl enol ether, followed by an intramolecular Michael addition and subsequent elimination of methanol. If the reaction was terminated by dilute ammonium chloride solution, then the Mannich bases 163 could be isolated and further transformed to the dehydropiperidinones 164 by treatment with dilute hydrochloric acid. This result proved that the reaction pathway is not a concerted hetero Diels-Alder type process between the electron-rich diene and the activated imine. The use of hydrogen chloride as a terminating agent resulted in exclusive isolation of the piperidine derivatives 164 formed with... 

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