Cobalt-catalyzed reactions chloride

Not only do palladium complexes catalyze reactions of Eq. (58), but nickel complexes were also effective (51) and formed the same products. Complexes such as Fe(CO)5 and Fe2(CO)8 were ineffective. Cobalt carbonyl, and tris-triphenylphosphinerhodium chloride were effective even at room temperature, but no 2 1 adducts were made. With both palladium and nickel, the activity of the catalyst and the distribution of products between 1 1 and 2 1 adducts is greatly dependent on the nature of the donor ligands on the metal. 

Recently, Oshima has reported a cobalt-catalyzed allylzincation of internal alkyne derivatives (Scheme 10). Optimization of the reaction leads to utilization of cobalt(ll) chloride in THF at room temperature. No traces of regio- and stereoisomers are obtained. The resulting alkenylzinc species 34 can be trapped with a large number of electrophiles in order to generate stereoselectively the tri- and tetrasubstituted alkenes 35-37. 

As recently reported, cobalt-catalyzed addition of olefins to butadiene is probably an example of the addition of cobalt alkyls to butadiene (106). The catalyst was the type prepared by reaction of cobalt chloride with an aluminum alkyl in the presence of a diene. A bis-7r-allylcobalt derivative is probably formed. The unstable 7r-allylcobalt compounds probably decompose (reversibly) into cobalt hydride. The hydride would add to the olefin present to form a dialkyl, which could then add again to the diene. 

Ionic and free-radical reactions leading to the formation of ketonic products can occur simultaneously in the copper-catalyzed reaction of a Grignard reagent with a sterically hindered acid halide. These reactions have been studied by Dubois and co-workers 102-108, 194). Contrary to the report of Percival et al. 229), ferric chloride inhibits the catalytic role of copper and does not favor the formation of ketones 106, 108). The scheme depicted in Fig. 4 is proposed 103) to account for the products of the reaction. Similar radical reactions were suggested by Khar-asch et al. 169) to explain the role of cobalt chloride in like reactions. 

As already mentioned, the second system to be studied [116] was the 5-norbornenyl system. The radical clock-5-norbornenyl 149 [118] is known to rearrange to the 3-nortricyclenyl radical with a rate constant, determined by EPR, on the order of 6 x 10 sec at -30 C and 10 -10 see" at 25 C [123, 124]. It has been firmly established from numerous examples of free radical reductions involving this system that the equilibrium in solution is in favor of radical 150. For example, a report by Davies [125] demonstrated that whether one started from 5-bromo-2-norbornene 148 Br or from 3-bromonortricyclene 153 Br when carrying out a cobaltous chloride-catalyzed reaction with methylmagnesium bromide, one obtains a mixture of 30% 2-norbornene 151 and 70% norticyclene 152 (Scheme 45a). 

Complexes of many transition metals including cobalt, rhodium, iridium, iron, nickel, palladium, and platinum have been found to catalyze double-bond migration in terminal olefins. Evidence for a mechanism of the following type, which is probably also applicable to some of the other catalysts, has been obtained by Cramer 24, 27) for the rhodium chloride-catalyzed reaction (Reaction 37). 

Kom, T. J., Cahiez, G., Knochel, P. New cobalt-catalyzed cross-coupling reactions of heterocyclic chlorides with aryl and heteroaryl magnesium halides. Syn/etf 2003,1892-1894. 

The realization that doubly carbonylated products can be formed in carbonylation reactions has only emerged in the last ten years, but specific syntheses of many a-keto acids, amides, esters and related products are being developed rapidly. Although many such syntheses depend on the use of CO pressures well above ambient, variation of other parameters such as catalyst, solvent and base can lead to efficient double carbonylation even at relatively low pressures. Selective, cobalt-catalyzed formation of phenylpy-mvic acid (97% selectively at 85% yield) from benzyl chloride was thus achieved at 50 bar pressure of CO in propan-2-ol, but more recent work has shown that similar selectivity and an even higher yield can be obtained at less than 2 bar when 1,2-dimethoxyethane is used as solvent (equation 62). °°... 

A method complementary to the palladium-catalyzed reaction has been reported. A cobalt-phosphine complex catalyzes a Heck-type reaction of alkyl halides with styrenes in the presence of Me3SiCH2MgCl [174]. Trimethylsilylmethylmag-nesium chloride was added to a mixture of styrene and bromocyclohexane in ether in the presence of a catalytic amount of CoCl2(dpph) at O C. Heating the reaction mixture under reflux (35°C) provided 163a in 91% yield (Scheme 3.158). 

The catalyst PdO (0.020 g 0.16 mmol), [M(CO) ] (2.0 mmol M = Cr, 0.440 g M = Mo, 0.528 g M = W, 0.704 g), and toluene (40 mL) are combined in the reaction flask. The mixture is heated to boiling and the appropriate amount of tert-butylisocyanide required to achieve mono-(2.05 mmol, 0.230 mL), di- (4.1 mmol, 0.460 mL), or trisubstitution (6.15 mmol, 0.690 mL) is added by microsyringe. The reaction mixture is heated under reflux until completion of the reaction as monitored by IR spectroscopy or thin layer chromatography (Table I). The mixture is allowed to cool to room temperature and Altered through a fluted filter paper to separate the catalyst. The solvent is removed under vacuum to give the crude products. Product purification employed the same procedures detailed above for the cobalt(II) chloride-catalyzed reaction. ... 

Cobalt catalysis has also received increased attention [351, 352]. Cobalt-catalyzed heterobiaryl coupling reactions between aryl chlorides and arylmagnesium halides take place with low loadings of Co(acac)j as the precatalyst under mild conditions [353]. Kinetic studies indicate that the active catalyst is an arylcobaltate(I) species. 

In parallel to their work on the cobalt-catalyzed alkylation of secondary ben-zamides with alkyl chlorides (Scheme 19.36) [57], Nakamura and coworkers [71] reported a seemingly similar method with alkyl Grignard s reagents as the alkyl donors (Scheme 19.45). The reaction occurred at room temperature and under air, and furnished the mono- or bis-alkylated product selectively depending on the amide substituent. It was found to be also applicable to phenylpyridines and benzo[k]quinoline. 

Okamoto and coworkers reported a cobalt-catalyzed cycloaddition reaction of nitriles and a,cobalt chloride hexahydrate (C0CI2 6H2O)/ zinc-catalyzed [2 -I- 2 + 2] cycloaddition reaction from the corresponding substrates with excellent regioselectivity (Scheme 3.10). More specifically, symmetrical and unsymmetrical 1,6-diynes and 2-cyanopyridine reacted in the presence of 5 mol% of dppe, 5 mol% of... 

The reaction of epoxides with styrene provides homocin-namyl alcohols in good yield (eq 34). The reaction involves ring-opening of the epoxide to yield the magnesium alkoxide of a vtc-halohydrin, which then undergoes the cobalt-catalyzed styrylation. Use of trimethylsilylmethylmagnesium bromide and cobalt(II) bromide, instead of chlorides, facilitates the reaction of epoxide since the more nucleophilic bromide efficiently attacks the epoxide. Conversion of tosylaziridines affords homocinnamyl amines. 

Then, the use of nickel(II) or cobalt(II) complexes as catalyst associated to the sacrificial anode process allows synthesis of functionalized mono- or diorganozinc species in a simple and efficient manner. Alternating Jt-conjugated copolymers, based on this electrochemical preparation of intermediate aryldizinc species and their subsequent palladium-catalyzed coupling with unsaturated dihalogenated compounds, can be synthesized. Furthermore, aromatic ketones are synthesized efficiently via cobalt-catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. 

Carbonyiation of butadiene gives two different products depending on the catalytic species. When PdCl is used in ethanol, ethyl 3-pentenoate (91) is obtained[87,88]. Further carbonyiation of 3-pentenoate catalyzed by cobalt carbonyl affords adipate 92[89], 3-Pentenoate is also obtained in the presence of acid. On the other hand, with catalysis by Pd(OAc)2 and Ph3P, methyl 3,8-nonadienoate (93) is obtained by dimerization-carbonylation[90,91]. The presence of chloride ion firmly attached to Pd makes the difference. The reaction is slow, and higher catalytic activity was observed by using Pd(OAc) , (/-Pr) ,P, and maleic anhydride[92]. Carbonyiation of isoprcne with either PdCi or Pd(OAc)2 and Ph,P gives only the 4-methyl-3-pentenoate 94[93]. 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

A combination of chiral cobalt-catalyst and sodium borohydride was successfully applied to the asymmetric reduction of aromatic ketones. A chiral cobalt complex 164 (5 mol%), prepared from the corresponding salen-type chiral bisketoaldimine and cobalt(II) chloride, catalyzed the reduction of dimethylchromanone 165 in the presence of sodium borohydride (1.5 equiv to ketone) in chloroform, including a small amount of ethanol at -20°C for 120 h to give alcohol 166 92% ee (S ) in 94% yield (Scheme 2.18) [94], Addition of tetrahydrofurfuryl alcohol (THFFA) to the reaction system or the use of pre-modified borohydride, NaBH2(THFFA)2, improved the catalyst activity, that is, using this protocol, the reactions of ketone 165 and... 

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