Radical cross-coupling reaction

The introduction of a styryl group at the C-6 position of penams finds its application in the intrinsic /3-lactamase inhibition activity of 6-vinyl penicillins 26 (see Sections 2.03.5.9 and 2.03.12.4). Its incorporation can be performed via a cobaltoxime-mediated radical cross-coupling reaction between a 6-bromopenicillanate and styrene (Scheme 15) < 1996BML2289>. 

Scheme 15 Cobaltoxime-mediated radical cross-coupling reaction.

Due to the similarity of the intermediate polymer radicals, cross-coupling reactions should occur when reactions (1) and (4) are run simultaneously for example ... 

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

In contrast to the transition metals, where there is often a change in oxidation level at the metal during the reaction, there is usually no change in oxidation level for boron, silicon, and tin compounds. The synthetically important reactions of these three groups of compounds involve transfer of a carbon substituent with one (radical equivalent) or two (carbanion equivalent) electrons to a reactive carbon center. Here we focus on the nonradical reactions and deal with radical reactions in Chapter 10. We have already introduced one important aspect of boron and tin chemistry in the transmetallation reactions involved in Pd-catalyzed cross-coupling reactions, discussed... 

Branchaud and coworkers have used cobaloximes as alkyl radical precursors for the cross-coupling reaction with nitronates.57 This method is very useful for producing branched-chain monosaccharides, as shown in Eq. 5.39.57b... 

It is considered that the stannyl or silyl radical and the alkyl radical are reactive intermediates in these reactions. In contrast to the selective formation of the arylchalcogenosilanes in the above radical reactions, the cross-coupling reaction of a hydrosilane with alkyl(aryl)sulfides catalyzed by palladium nanoparticles results in the selective formation of the corresponding alkylthiosilanes.42... 

Cross coupling reactions, for example between 9-phenylanthracene radical-cation and anisole or toluene are known. 9-Phenylanthracene is more easily oxidised than anisole or toluene and carbon-carbon bond formation takes place by reaction between 9-phenylanthracene radical-cation and the substituted benzene. These reactions follow a kinetic scheme related to that of Scheme 6.3(b) in which a second electron transfer step is rate determining, although an inverse dependence of the rate on the concentration of 9-phenylanthracene can be detected [28],... 

By contrast, for iodide 18 having the triple bond activated by a phenyl group, conversion to the cyclic organozinc species 25 occurred effectively and the latter could be efficiently functionalized, provided that traces of moisture were excluded by pre-treatment of zinc powder with Mel. The substituted benzylidene cyclopentanes 26 and 27 were respectively obtained after iodinolysis and palladium-catalyzed cross-coupling reaction with benzoyl chloride (equation 10). However, it could not be assessed whether the formation of organozinc 25 was attributable to an anionic or a radical cyclization pathway (or both) as, had iodide 26 been produced by a radical iodine atom-transfer, it would have been converted to 25 by reaction with metallic zinc due to the presence of the activating phenyl group21. 

For kinetic purposes, acetylperoxyl radicals were generated by laser flash photolysis of an acetylcobalt precursor in the presence of 02, Eq. (26). With use of ABTS - as a kinetic probe, the rate constant was determined for the cross-coupling reaction of Eq. (27), 27 = 1.49 x 108 M 1 s-1. 

Halogen functionality in heteroaromatics undergoes a variety of transformations by nucleophilic substitution metal-halogen exchange, radical substitution, and cross coupling reactions. The connecting link between these processes and the DoM reaction is therefore a powerful tool in heterocyclic chemistry. 

Considering the racemization in the cross-coupling process of enantiomerically pure alkyl halides (Table 5.8, entry 18), Fiirstner et al. partially support a theory delineating a metal-bound radical. However, they also call attention to several compounds set up for analogous 5-exo-trig cyclizations but that do not cyclize under identical conditions of the cross-coupling reaction [Scheme 5.18, reaction (3)]. Consequently, care has to be taken in generalizing this mechanistic proposal. 

Alkenylboron compounds cyclopropanations, 9, 181 haloetherification, 9, 182 hydrogenation and epoxidation, 9, 182 metal-catalyzed reactions, 9, 183 metallic reagent additions, 9, 182 via radical addition reactions, 9, 183 5-Alkenylboron compounds, cross-coupling reactions, 9, 208 Alkenyl complexes with cobalt, 7, 51 with copper, 2, 160, 2, 174 with Cp Re(CO) (alkene)3 , 5, 915-916 with dicarbonyl(cyclopentadienyl)hydridoirons, 6, 175 with gold, 2, 255... 

The exocyclic C(2)-S bond of a 2-thiopenem 50 can undergo radical reactions. As depicted in Scheme 28, its desulfurative stannylation reaction with azobis(isobutyronitrile) (AIBN) and tributyltin hydride leads to a penem stannane 51 <1995TL775>. The latter allows subsequent palladium(0)-mediated cross-coupling reactions with... 

Abstract Increasing reaction speed and simplifying product purification are two major ways to improve the efficiency of organic synthesis. A new technology for high-speed solution-phase synthesis has been developed by combination of microwave heating and fluorous purification. This review describes different techniques for microwave-enhanced fluorous synthesis and their applications in Pd-catalyzed cross-coupling reactions, free-radical reactions, multicomponent reactions, and compound library synthesis. 

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