Proton Affinities of Organocatalysts Derived from Pyridine N-oxide

Proton affinities of several efficient organocatalysts METHOX, QUINOX, ANETOX, KOTOX, FUREOX, and FUROOX bearing a pyridine N-oxide or 2,2′-bipyridyl N,N′-dioxide moiety were de-termined by using extended kinetic method and density functional theory calculations. Proton affinities are in the range of 1030–1060 kJ mol–1. Using isodesmic reactions, the effect of combining two pyridine N-oxide units in the neutral and the protonated molecule was studied: The combination of an unfavorable interaction in the former case and a favorable interaction in the latter accounts for the superbasic proper¬ties of 2,2′-bipyridyl N,N′-dioxides. Last but not least, the theoretically predicted pKa in ethanol are 0.1, –2.7, 0.9, 1.8, 1.9, and 2.3 for the METHOX, QUINOX, ANETOX, FUROOX, FUREOX, and KOTOX, respectively

2,8'-Disubstituted-1,1'-Binaphthyls:A New Pattern in Chiral Ligands

The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2'-(diphenylphosphino)-1,1'-binaphthyl (MOP, 19) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15→18), followed by functional group transformations, involving C-P and C-N bond formation (18→19 and 18→23). Racemic intermediate 22 was resolved by cocrystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(-)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92% ee (after hydrolysis of the primary product)

Synthesis of γ-functionalized allyltrichlorosilanes and their application in the asymmetric allylation of aldehydes

Isomerically pure trans- and cis-γ-bromoallyltrichlorosilanes 4 and 5 have been synthesized and shown to react with aromatic aldehydes 1 in the presence of Lewis-basic catalysts (e.g., DMF) to produce the corresponding anti- and syn-allylbromohydrins 8 and 9, respectively, as single diastereoisomers. With BINAPO 25 as a chiral catalyst, promising enantioselectivity (⩽50% ee) has been attained

Bile acids: Electrochemical oxidation on bare electrodes after acid-induced dehydration

Bile acids and sterols in general have long been considered practically inactive for direct redox processes. Herein, a novel way of electrochemical oxidation of primary bile acids is reported, involving an initial acid-induced dehydration step, as confirmed by capillary electrophoresis–mass spectrometry, thereby extending the electrochemical activity of the steroid core. Oxidation potentials were found to be ca +1.2 V vs. Ag/AgNO3 in acetonitrile on boron doped diamond, glassy carbon, and platinum electrodes in a mixed acetonitrile–aqueous medium employing perchloric acid as a chemical reagent, and as a supporting electrolyte for the voltammetric measurements. The chemical step proved to be effective only for primary bile acids, possessing an axial 7α-hydroxyl group, which is a prerequisite for providing a well-developed voltammetric signal. Preliminary results show that other steroids, e.g., cholesterol, can also be oxidized by employing a similar approach. Keywords: Bile acids, Steroid dehydration, Electrochemical oxidation, Bare electrode, Voltammetr