Oxidative coupling with base

In the past, TTF has been prepared from 1,3-dithiole-2-thione, which, by an oxidative step, was converted to a 1,3-dithiolylium salt followed by coupling with base.6 9,15 The present method uses a reductive sequence, thereby permitting milder conditions and better yields.16... 

Oxidative coupling of aromatic compounds via the SchoU reaction has been appHed successhiUy to synthesise a polyarylethersulfone (18). High molecular weight polymer was obtained upon treating 4,4 -di(l-naphthoxy)diphenylsulfone and 4,4 -di(l-naphthoxy)ben2ophenone with ferric chloride. Equimolar amounts of the Lewis acid are required and the method is limited to naphthoxy-based monomers and other systems that can undergo the SchoU reaction. 

Work in the mid-1970s demonstrated that the vitamin K-dependent step in prothrombin synthesis was the conversion of glutamyl residues to y-carboxyglutamyl residues. Subsequent studies more cleady defined the role of vitamin K in this conversion and have led to the current theory that the vitamin K-dependent carboxylation reaction is essentially a two-step process which first involves generation of a carbanion at the y-position of the glutamyl (Gla) residue. This event is coupled with the epoxidation of the reduced form of vitamin K and in a subsequent step, the carbanion is carboxylated (77—80). Studies have provided thermochemical confirmation for the mechanism of vitamin K and have shown the oxidation of vitamin KH2 (15) can produce a base of sufficient strength to deprotonate the y-position of the glutamate (81—83). 

The boronic acid 2 is first converted to an activated species 8 containing a tetravalent boron center by reaction with a base. Halides or triflates (OTf = trilluoromethanesulfonate) are used as coupling partners R-X for the boronic acids. In many cases the rate-limiting step is the oxidative addition. With respect to the leaving group X, the rate decreases in the order ... 

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

When oxidized by iron(III) ions 4-aminoantipyrine reacts with phenols to yield colored quinonoid derivatives (cf. 4-aminoantipyrine — potassium hexacyanoferrate(III) reagent in Volume 1 a). It is an oxidative coupling based on the Emerson reaction. 

The chemistry of vinyl acetate synthesis from the gas-phase oxidative coupling of acetic acid with ethylene has been shown to be facilitated by many co-catalysts. Since the inception of the ethylene-based homogeneous liquid-phase process by Moiseev et al. (1960), the active c ytic species in both the liquid and gas-phase process has always been seen to be some form of palladium acetate [Nakamura et al, 1971 Augustine and Blitz, 1993]. Many co-catalysts which help to enhance the productivity or selectivity of the catalyst have appeared in the literature over the years. The most notable promoters being gold (Au) [Sennewald et al., 1971 Bissot, 1977], cadmium acetate (Cd(OAc)j) [Hoechst, 1967], and potassium acetate (KOAc) [Sennewald et al., 1971 Bissot, 1977]. 

Madsen and co-workers have reported an important extension to the amine alkylation chemistry, in which oxidation takes place to give the amide product [13]. A ruthenium NHC complex is formed in situ by the reaction of [RuCl Ccod)] with a phosphine and an imidazolium salt in the presence of base. Rather than returning the borrowed hydrogen, the catalyst expels two equivalents of H. For example, alcohol 31 and benzylamine 27 undergo an oxidative coupling to give amide 32 in good isolated yield (Scheme 11.7). 

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