Coupling reactions Nickel carbonyl

Nickel carbonyl effects coupling of allylic halides when the reaction is carried out in very polar solvents such as DMF or DMSO. This coupling reaction has been used intramolecularly to bring about cyclization of to-allylic halides and was found useful in the preparation of large rings. 

Carbonylation is an exceedingly broad subject, but the main reaction patterns can be easily rationalized by recalling the classification used earlier for coupling reactions involving (a) metallacycles (b) hydride-promoted reactions and (c) oxidative addition of organic halides to zero-valent nickel. In fact, one or other of these steps is necessary to form a species able to undergo carbonylation. 

Recently, four-component coupling reactions of aldehydes, alkynes, dienes, and dimethylzinc catalyzed by a nickel complex have been reported (Equation (78)).435 Similarly, l,c< -dienynes react with carbonyl compounds and dimethylzinc in the presence of an Ni catalyst to afford the corresponding cyclized products. 

Two recently developed coupling reactions of an alkene (R1CH2CH=CH2), an aldehyde (R2CHO), and a silyl triflate (R33SiOTf) yield an allylic (66) or homoallylic (67) alcohol (in protected form).188 Employing nickel-phosphine catalysts, either product can be selected by small changes in the phosphine component. A mechanism distinct from that of Lewis acid-catalysed carbonyl-ene reactions is proposed and discussed. 

A nickel-catalysed alkyne insertion between the carbonyl carbon and the -carbon of the cyclobutanone was achieved by combining a ketone-alkyne coupling reaction with a /3-carbon elimination process (Scheme 79).121 The reaction uses cyclobutanones as a four-carbon unit and provides access to substituted cyclohexenones. 

As discussed in Section I, the reaction of ally lie halides with nickel carbonyl at atmospheric pressure leads to coupling products or in some cases, in hydroxylic solvents, to substitutive hydrogenation (34). Under... 

Benzyl halides have been reported to react with nickel carbonyl to give both coupling and carbonylation (59). Carbonylation is the principal reaction in polar nonaromatic solvents, giving ethyl phenylacetate in ethanol, and bibenzyl ketone in DMF. The reaction course is probably similar to that of allylic halides. Pentafluorophenyl iodide gives a mixture of coupled product and decafluorobenzophenone. A radical mechanism has been proposed (60). Aromatic iodides are readily carbonylated by nickel carbonyl to give esters in alcoholic solvents or diketones in ethereal solvent (57). Mixtures of carbon monoxide and acetylene react less readily with iodobenzene, and it is only at 320° C and 30 atm pressure that a high yield of benzoyl propionate can be obtained (61). Under the reaction conditions used, the... 

Bicyclic ketones are prepared by cycloadditions of methylenecyclopropanes with cyclic a,P-unsatu-rated carbonyl compounds. c J-Bicyclo[3.3.0]octan-2-ones (50), (51) and (52) are obtained in good yields by phosphine-nickel(0)-catalyzed cross coupling reactions of 2-cyclopentenone with methylenecyclopropanes in the presence of 0.1-1 equiv. of triethylborane as a Lewis acid (equations 18 and 19 and... 

Synthesis of maerolides. The intramolecular coupling reaction of allylic halides (I, 722-723 2, 290-292 3, 211) has now been shown to be applicable to the synthesis of maCrocyclic lactones. Thus addition of the dibromo ester (1) to 6 eq. of nickel carbonyl in N-methylpyrrolidone effects cyclization to the macrolide (2) as the major product. 

Carborane-metal complexes, 8, 87-113 Catalysis by organometallics carbonylation, 6, 158-163 hydroformylation, 6, 128-136 olefin reactions, 7, 199-202 organic syntheses by nickel compounds, 8, 48-83 reviews, 10, 331-336 Cationic metal carbonyls, 8, 117-159 Chromium carbonyls, 8, 133-159, see also Benchrotrenes Cobaloximes, 7, 161, 203 Cobalt carbonyl, 6, 119-163 8, 152-155 Cotton-Kraihanzel method, 10, 213-214 Coupling reactions, on nickel, 8, 30-39, 82-83... 

Coupling of allylic halides. Hall and Hurley1 have confirmed patent claims that allylic halides can be coupled by iron powder the nature of the solvent is highly important. The dipolar aprotic solvent DMF was found most satisfactory. Added inorganic bromide or iodide salts exert a marked catalytic effect. In favorable cases 90% yields of nonconjugated dienes can be obtained. In recent times nickel carbonyl has been used extensively for this coupling reaction (1, 722-723 2,290-292) however, nickel carbonyl is highly toxic and flammable. 

Intramolecular allylic coupling (1, 722-723 2, 290-292). The key step in a total synthesis of the sesquiterpene elemol (3) involves reaction of the dibromo ester (1) with nickel carbonyl (7 equiv.) in N-methylpyrrolidone to form the monocyclic ester (2). Several other products are obtained, separable by chromatography. Significantly none of the c/ -adduct is formed. Reaction of (2) with... 

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