Self-coupling

An elegant synthesis method which is specific to sulfone polymers containing phenyl—phenyl linkages (such as PPSF) is the nickel-catalysed coupling of aryl dihahdes. The scheme for this synthesis involves a two-step process. First, an aromatic dihaUde intermediate is formed which carries the backbone features of the desired polymer. This aromatic dihahde intermediate is then self-coupled in the presence of sero-valent nickel, triphenylphosphine, and excess sine to form the biphenyl- or terphenyl-containing polymer. AppHcation of this two-step scheme to PPSF can be depicted as follows ... 

Similarly, aromadc Grignaid reagents undeiga free-radical self-coupling reactions when treated with MCI2 (M=Cr, Mn, Ft, Co, Ni), e.g. ... 

In Ghosh s enantioselective total synthesis of the cytotoxic marine macrolide (+)-amphidinolide T1 (318) [143], the C1-C10 fragment 317 was constructed by CM of subunits 315 and 316 (Scheme 62). The reaction mediated by catalyst C (5 mol%) afforded in the first cycle an inconsequential 1 1 mixture of (E/Z)-isomeric CM products 317 in 60% yield, along with the homodimers of 315 and 316. The self-coupling products were separated by chromatography and exposed to a second metathesis reaction to provide olefins 317 in additional 36% yield [144]. 

Gonzalez-Arellano, C., Corma, A., Iglesias, M. and Sanchez, F. (2005) Homogeneous and heterogenized Au(III) Schiff base-complexes as selective and general catalysts for self-coupling of aryl boronic acids. Chemical Communications, (15), 1990. 

Some effects of thermal instability have been noted [Eqs. (32) and (59)]. Formation of coupling products, e.g., biaryls, has sometimes been attributed to thermally induced self-coupling of organometallics formed by decarboxylation (1,20). 

Reaction of allyl nalides with the iron powders is rapid and exothermic and leads to near quantitative yields of the self-coupled product 1,5-hexadiene. Similarly, reaction of benzyl chloride with the iron powders at room temperature yields bibenzyl in 60-70% yields along with 20-25% of toluene. In contrast, reaction of aryl halides with the iron powders leads to reductive cleavage rather than self-coupling. Similarly, reaction of 1-bromoheptane with the iron powder in THF for three hours at room... 

A rapid self coupling reaction of /i-naphthols occurs in presence ofiron(III) chloride, FeCl3.6H20, using a focused MW oven under solvent-free conditions and is superior to classical heating mode [113]. 

Sumetsky, M. Dulashko, Y. Hale, A., Fabrication and study of bent and coiled free silica nanowires Self coupling microloop optical interferometer, Opt. Express 2004,12, 3521 3531... 

A first turning point in the dichotomy between radical and ionic chemistry is located at the level of the primary radical, usually an ion radical, formed upon single electron transfer to the substrate. If, for a reduction, the reaction medium is not too acidic (or electrophilic), and for an oxidation, not too basic (or nucleophilic), radical reactions involving the primary radical, such as self-coupling, have a first opportunity to compete successfully with acid-base reactions. In this competition, the acidity (for a reduction) or basicity (for an oxidation) of the substrate should also be taken into account insofar as they may lead to father-son acid-base reactions. It should also be taken into consideration that the primary radical may undergo spontaneous acid-base reactions such as expelling a base (or a nucleophile) after a reduction, and an acid (or an electrophile) after an oxidation. 

The study on the reaction of several ring-substituted anilines with HS in aqueous solutions showed that the free radical intermediates were converted to stable products by self-coupling or cross-coupling with other radical species (i. e., indigenous humic free radicals becoming incorporated into the HS macromolecule). 

The only reactions of diazoazoles with electrophiles are those with acids. The reaction with acids at room temperature or below has already been reviewed in the section on diazo-diazonium equilibrium. This section includes reported reactions occuring at higher temperatures which generally resulted in decomposition and/or self-coupling reactions. 

Diazo-5-phenyl-1,2,4-triazole reacted with methylamine to give the corresponding triazene (83JHC1629). Triazeno polymer 240 was formed by a self-coupling reaction of the diazotriazole obtained from guanazole... 

JOC3449) (Scheme 68). Diazotization of 238 in hydrochloric acid did not lead to the polymer. In acetic acid, the intermediate nitrosoamino derivative 239 was isolated. By action of hydrochloric acid and subsequent neutralization, 239 was converted into the diazo compound that immediately self coupled. 

Under the Suzuki reaction condition and in the presence of 2,3-bis(bro-momethyOquinoxaline 149, Song unexpectedly discovered that 140 was able to provide the self-coupling product, namely bifuran 150 in excellent yield (Scheme 31). Similarly, 150 produced quaterfuran 152 via 151, from which taliiran 153 was also obtained via a cross-coupling with 144 under identical conditions (Scheme 31). A variety of symmetrical and unsymmetrical furan-3,4-diyl oligomers were... 

The self-coupling mechanism still remains unclear, although its synthetic options appear to be rather encouraging. Mechanistically, it is likely that Pd(IV) intermediates were involved. ... 

An ingenious experimental example for the reverse of the socalled la coupe de Roi (i.e. the dividing of finite geometric objects into isometric segments) — namely the assembly of two homochiral compounds into an achiral one — was provided by making use of appropriate [2.2]metacyclophanes. Whereas self-coupling of (+)-4-(bromomethyl)-6-(mercaptomethyl)[2.2]metacyclophane (cf. formulas 55 to 60 for... 

The symmetry of this hydrocarbon makes possible a self-coupling reaction with 2-bromo-2-phenylpropane. 

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