Oxidative addition regioselectivity

For trisubstituted olefins, the nucleophile attacks predominantly at the less substituted end of the allyl moiety, e.g. to afford a 78 22 mixture of 13 and 14 (equation 7). Both the oxidative addition of palladium(O) and the subsequent nucleophilic attack occur with inversion of configuration to give the product of net retention7. The synthesis of the sex pheromone 15 of the Monarch butterfly has been accomplished by using bis[bis(l,2-diphenylphosphinoethane)]palladium as a catalyst as outlined in equation 87. A substitution of an allyl sulfone 16 by a stabilized carbon nucleophile, such as an alkynyl or vinyl system, proceeds regioselectively in the presence of a Lewis acid (equation 9)8. The... 

The event, oxidative addition of a Ni(0) species upon dienes and aldehydes activated by coordination with Lewis acids to provide oxanickellacycles 45, has proven to take place quite generally, and many variations making the best use of the intermediate 45 have been developed. The key issue of the reactions discussed in Sect. 3 is a regioselective and stereoselective hydrogen delivery... 

The mechanism for the reaction catalyzed by cationic palladium complexes (Scheme 24) differs from that proposed for early transition metal complexes, as well as from that suggested for the reaction shown in Eq. 17. For this catalyst system, the alkene substrate inserts into a Pd - Si bond a rather than a Pd-H bond [63]. Hydrosilylation of methylpalladium complex 100 then provides methane and palladium silyl species 112 (Scheme 24). Complex 112 coordinates to and inserts into the least substituted olefin regioselectively and irreversibly to provide 113 after coordination of the second alkene. Insertion into the second alkene through a boat-like transition state leads to trans cyclopentane 114, and o-bond metathesis (or oxidative addition/reductive elimination) leads to the observed trans stereochemistry of product 101a with regeneration of 112 [69]. 

The most plausible mechanism proceeds through oxidative addition of the aldehyde to an active Ru(0) species to form (acyl)(hydrido)ruthenium(ll) complex 155. Insertion of the less-substituted double bond of the 1,3-diene into the Ru-H bond occurs to generate an (acyl)( 73-allyl)ruthenmm(ll) intermediate of type 156. Successive regioselective reductive eliminations between the acyl and the 73-allyl ligands provide the desired product with regeneration of the... 

Cyclization of 2-(l-alkynyl)XV-alkylidene anilines is catalyzed by palladium to give indoles (Equation (114)).471 Two mechanisms are proposed the regioselective insersion of an H-Pd-OAc species to the alkyne moiety (formation of a vinylpalladium species) followed by (i) carbopalladation of the imine moiety and /3-hydride elimination or (ii) oxidative addition to the imino C-H bond and reductive coupling. 

A mechanistic pathway is proposed based upon the observed regioselectivities and other results that were obtained during the exploration of the scope and limitations of the Alder-ene reaction.38 Initially, coordination of the alkene and alkyne to the ruthenium catalyst takes place (Scheme 5). Next, oxidative addition affords the metallocycles 42 and 43. It is postulated that /3-hydride elimination is slow and that the oxidative addition step is reversible. Thus, the product ratio is determined by the rate at which 42 and 43 undergo /3-hydride elimination. 

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

The proposed mechanism is illustrated in Figure 8-5.60a Oxidative addition of the phenyl triflate to the palladium(0)-BINAP species A gives phenylpalla-dium triflate B. Cleavage of the triflate and coordination of 2,3-dihydrofuran on B yields cationic phenyl palladium olefin species C. This species C bears a 16-electron square-planar structure that is ready for the subsequent enantio-selective olefin insertion to complete the catalytic cycle (via D, E, F, and G). The base and catalyst precursor have profound effects on the regioselectivity and enantioselectivity. 

In one possible mechanism, oxidative addition of iodobenzene to Pd(0) gives Pd(II) intermediate 74, which subsequently inserts into thiazole regioselectively at the C(5) position to form the a-adduct of arylpalladium(II) 75. The order of reactivity is similar to the electrophilic substitution, which is known to be C(5) > C(4) > C(2) [74]. Treatment of the insertion adduct 75 with a base regains the aromaticity after deprotonation, giving rise to 73 along with Pd(0) for the next catalytic cycle. 

Diketones. Some years ago Heiba and Dessau reported that Mn(OAc), promotes oxidative addition of isopropenyl acetate to ketones to give 1,4-diketones in 20-35% yield (6, 356). Use of CAN as the oxidant results in higher yields (65-80%) and a regioselective reaction at the more substituted a-position of the ketone.1 Use of vinyl acetate results in the dimethyl acetal of 4-oxo aldehydes. 

Vitamin Bi2-catalyzed intramolecular cathodic coupling leads to a regioselective 1,4-addition with formation of a spirocom-pound (Eq. 2) [95]. This chain reaction is initiated by the reduction of Co(III) to a Co(I) species, which reacts in an oxidative addition with the alkyl bromide. The resulting alkyl-Co(III)-Br species is then reduced to an alkyl anion that undergoes a Michael addition and yields Co(I) for the next cycle. 

Regioselective syntheses of 1,3,5-unsymmetrically substituted benzenes (309) are catalyzed by Pd(dba)2/PPh3 mixed alkyne/diyne reactants give mixtures containing homocoupled and mixed products (24 21 from HC CPh + HC=CC= CC Hn). The probable mechanism involves oxidative addition to the Pd(0) center, insertion of the second diyne into the Pd—H bond, reductive coupling and subsequent jr-complexation of this product to Pd(0), followed by Diels-Alder cycloaddition of the third diyne and elimination of product. 

It is assumed that the reaction proceeds by the oxidative addition of the carbon-carbon bond of the cyclopropane to cobalt species to form a metallacyclic intermediate. The regioselectivity of this reaction is controlled by the relative ease of insertion of the cobalt species into the C1-C2 and the C1-C3 bonds of the cyclopropane (Scheme 7). In the case of the reaction of the (1-R, 2k )-isomer trans-l5a, 5-methyl-3-phenyl-2-cyclopenten-1-one (17a) is produced via TS2 without any serious steric repulsion, while the 4-methyl isomer 16a must be pro-... 

Organoborane intermediates can also be used to synthesize alkyl halides. Replacement of boron by iodine is rapid in the presence of base.150 The best yields are obtained with sodium methoxide in methanol.151 If less basic conditions are desirable, the use of iodine monochloride and sodium acetate gives good yields.152 As is the case in hydroboration-oxidation, the regioselectivity of hydroboration-halogenation is opposite to that observed for direct ionic addition of hydrogen halides to alkenes. Terminal alkenes give primary halides. 

Arylated 5-chloro-2-methylpyridazin-3(277)-ones could be accessed regioselectively by exploiting the difference in reactivity of the C-Cl and the C-I bond of 186 in an oxidative addition reaction (Equation 36) <2005JHC427>. 

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