Competitive coupling derivatives

Other benzyl radicals, including the parent benzyl radical, give reversible formation of quinonemethide derivatives (typically a mixture of a,p- and cqocoupling products) in competition with a,a-coupling (see also Section... 

Thus far, the use of acrylates and related acyl derivatives as nucleophilic partners in hydrogen-mediated reductive aldol coupling has been unsuccessful due to competitive conventional hydrogenation. Although the mechanistic basis of these results remains unclear, it may be speculated that for acrylates and struc-... 

A number of rate constants for reactions of transients derived from the reduction of metal ions and metal complexes were determined by pulse radiolysis [58]. Because of the shortlived character of atoms and oligomers, the determination of their redox potential is possible only by kinetic methods using pulse radiolysis. In the couple Mj/M , the reducing properties of M as electron donor as well as oxidizing properties of as electron acceptor are deduced from the occurrence of an electron transfer reaction with a reference reactant of known potential. These reactions obviously occur in competition with the cascade of coalescence processes. The unknown potential °(M /M ) is derived by comparing the action of several reference systems of different potentials. 

Perfluoroalkylcopper reagents couple with 1-iadoacetylenic derivatives to give the expected perfluoroalky(-substituted acetylenes [226] (equation 153) The coupling reaction is complicated by formation of the diyne from competitive exchange processes... 

A stereochemical study of the synthesis of unsaturated 1,4-aminoalcohols via the reaction of unsaturated 1,4-alkoxyalcohols with chorosulfonyl isocyanate revealed a competition between an retentive mechanism and an SnI racemization mechanism, with the latter having a greater proportion with systems where the carbocation intermediate is more stable.254 An interrupted Nazarov reaction was observed, in which a nonconjugated alkene held near the dienone nucleus undergoes intramolecular trapping of the Nazarov cyclopentenyl cation intermediate.255 Cholesterol couples to 6-chloropurine under the conditions of the Mitsunobu reaction the stereochemistry and structural diversity of the products indicate that a homoallylic carbocation derived from cholesterol is the key intermediate.256 l-Siloxy-l,5-diynes undergo a Brpnsted acid-promoted 5-endo-dig cyclization with a ketenium ion and a vinyl cation proposed as intermediates.257... 

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