De-hydrogen-coupling

Friedel-Crafts Arylation. The Scholl Reaction De-hydrogen-coupling... 

Conversion of One Aromatic Compound to Another (6)cyc/o-de-hydrogen-coupling (Overall transformation)... 

The replacement of an electrofugic atom or group at a nucleophilic carbon atom by a diazonium ion is called an azo coupling reaction. By far the most important type of such reactions is that with aromatic coupling components, which was discovered by Griess in 1861 (see Sec. 1.1). It is a typical electrophilic aromatic substitution, called an arylazo-de-hydrogenation in the systematic IUPAC nomenclature (IUPAC 1989c, see Sec. 1.2). 

Reduction of Nitro to Hydrazo Compounds /V-Hydrogen-de-bisoxygen-coupling... 

Nickel metal catalysts give mixtures of the corresponding silyl ether and silyl enol ether. The former is produced via hydrosilylation, while the latter is produced via de-hydrogenative silylation. The reaction catalyzed by zinc chloride proceeds under drastic conditions, and the product of aldehydes disproportionates. The reaction of a,jS-unsatu-rated carbonyl compounds with H2PtCl6 proceeds by 1,4-addition, while coupling is also observed on using metallic Ni as catalyst. ... 

Asymmetric hydrogenation. Hydrogenation of the a-substituted /8-kcto ester 2 with a Ru(ll) catalyst coupled with (R)-l provides the desired /8-hydroxy ester 3 in 90% ec but with only moderate. vyrr-selectivity (74% de). Hydrogenation with high cnantio-and diastereosclectivity can be achieved using a BINAP derivative in which the phenyl... 

The first unequivocal evidence for the AE + DE mechanism came in three papers by Zollinger (1955 a-c) dealing with general base catalysis and primary kinetic hydrogen isotope effects in azo coupling reactions of various types. Three classes of reactions were identified i) reactions with no isotope effects (ArH/A D - 1.0) and no general base catalysis, ii) others with large isotope effects (k /k — 6.5) and (practically) linear base catalysis, and iii) intermediate cases with isotope effects of around 3.0 and less-than-linear base catalysis. 

Treatment of intermediate 31 with 2.2 equiv of 4-FB A in EtOH at 72 °C afforded 35 as a white crystalline solid in 90% isolated yield (Scheme 6.9). Hydrogenation in the presence of 5% of Pd/C and 1 equiv of MsOH, efficiently removed the Cbz-protected group. MsOH was used to prevent fluoride reduction resulting in low levels of the des-fluoro by-product. Catalyst filtration, followed by neutralization of the crude reaction mixture with NaOH, afforded free amine 36 as a white crystalline product in 99% isolated yield. Free-amine 36 was isolated as a dihydrate which necessitated drying prior to coupling with oxadiazole chloride 2. 

De Redge PJF, Williams SA, Therien MJ (1995) Direct evaluation of electronic coupling mediated by hydrogen bonds implications for biological electron transfer. Science 269 1409-1413... 

P. J. F. de Rege, S. A. Williams, M. J. Therien, Direct Evaluation of Electronic Coupling Mediated by Hydrogen Bonds - Implications for Biological Electron Transfer , Science 1995, 269,1409-1413. 

---