Nickel cyclization reactions

A cyclization reaction involving a half-formed bridge in which alkyl halide functions interact with (initially) coordinated oxygen atoms is illustrated by [2.9] (Kluiber Sasso, 1970). The X-ray structure of the red paramagnetic nickel complex (65) indicates that the macrocycle coordi-... 

Unlike nickel Catalysts, palladium complexes do not catalyze the homo-cyclization reaction to give CDT or COD. The difference seems to be due to a different degree of hydride shift and atomic volume. With palladium catalysts, the hydride shift is easier, and hence linear oligomers are formed. The characteristic reaction catalyzed by palladium is the cocyclization of two moles of butadiene with one-hetero atom double bonds such as C=N and C=0 bonds to give six-membered rings with two vinyl groups (19) ... 

Tamao and Ito have reported a nickel-catalyzed protocol for the cyclization/hydrosilylation of 1,7-diynes to form (Z)-silylated dialkylidene cyclohexane derivatives.For example, reaction of 1,7-octadiyne with triethoxysilane catalyzed by a mixture of Ni(acac)2 (lmol%) and DIBAL-H (2mol%) in benzene at 50°G for 6h gave the corresponding silylated dialkylidene cyclohexane in 70% yield as a single isomer (Table 1). The reaction of 1,7-octadiyne was also realized with mono- and dialkoxysilanes, trialkylsilanes, and dialkylaminosilanes (Table 1). Diynes that possessed an internal alkyne also underwent nickel-catalyzed reaction, albeit with diminished efficiency (Table 1), while 1,6- and 1,8-diynes failed to undergo nickel-catalyzed cyclization/hydrosilylation. 

Mori has reported the nickel-catalyzed cyclization/hydrosilylation of dienals to form protected alkenylcycloalk-anols." For example, reaction of 4-benzyloxymethyl-5,7-octadienal 48a and triethylsilane catalyzed by a 1 2 mixture of Ni(GOD)2 and PPhs in toluene at room temperature gave the silyloxycyclopentane 49a in 70% yield with exclusive formation of the m,//7 //i -diastereomer (Scheme 14). In a similar manner, the 6,8-nonadienal 48b underwent nickel-catalyzed reaction to form silyloxycyclohexane 49b in 71% yield with exclusive formation of the // /i ,// /i -diastereomer, and the 7,9-decadienal 48c underwent reaction to form silyloxycycloheptane 49c in 66% yield with undetermined stereochemistry (Scheme 14). On the basis of related stoichiometric experiments, Mori proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of dienals involving initial insertion of the diene moiety into the Ni-H bond of a silylnickel hydride complex to form the (7r-allyl)nickel silyl complex li (Scheme 15). Intramolecular carbometallation followed by O-Si reductive elimination and H-Si oxidative addition would release the silyloxycycloalkane with regeneration of the active silylnickel hydride catalyst. 

These palladium- or nickel-catalyzed reactions are radical reactions leading to an organometallic product. By using a precursor such as 37 as a 1 1 mixture of diastereoisomers, the palladium-catalyzed cyclization provides in a stereoconvergent way the cyclopentylmethylzinc derivative 38 which, after allylation, produces the unsaturated ester 39 in 71% yield". The intermediate radical cyclizes via a transition state A where all the substituents are in an equatorial position. Interestingly, the analogous reaction using Ni(acac)2 as a catalyst allows the preparation of heterocyclic compounds such as 40. The... 

Aldehydes constitute useful electrophilic partners in such nickel-catalyzed reactions because the condensation between alkynes, aldehydes and diorganozinc compounds can afford stereodefined cyclic or acyclic ally lie alcohols67-69, as illustrated by the stereoselective cyclization of 111 to the corresponding 3-hydroxypyrrolidine (equation 46). Allenes or 1,3-dienes instead of alkynes also lead to similar reactivity70. 

Formally, although these cyclooligomerizations can be considered as cycloaddition reactions, they are known not to occur through a direct cycloaddition process. In the best understood nickel-catalyzed reaction the dimer 12 was shown to be the key intermediate in cyclization.46,59 60 Acetylene readily undergoes cyclooligomerization in the presence of metal catalysts to form benzene and cyclooctatetraene [Eq. (13. 15)] as well as higher homologs ... 

The ligand (XIII Scheme 30) undergoes a cyclization reaction in the presence of Ni(N03)2 hydrate and gives the new ligand (XTV). Both ligands coordinate to nickel in the resulting mixed-ligand complex.2370... 

Aminobenzo[6]thiophene and its simple ring-substituted derivatives are most conveniently obtained by reduction of the corresponding nitro compound with tin and hydrochloric acid,883,334,544,545 iron and hydrochloric acid,555 ferrous sulfate and ammonia,185,330 333 334,497 sodium borohydride and palladized charcoal,337 cata-lytically,152, 422,488,543 or, preferably, with Raney nickel and hydrazine hydrate.152,298,338,497,556 Several 5-aminobenzo-[6]thiophenes may also be made by cyclization reactions (Section IV, D).239,330,331 333,494... 

In many of the above cyclization reactions it is not clear to what extent the metal ion is important. In most cases a geometrical effect is significant but electronic activation is probably not always of importance. The corphin synthesis (see Scheme 68) is a good example of precise geometrical requirements. This cyclization succeeds for the palladium complex but not for nickel or cobalt complexes. The imidate condensation seems to require steric acceleration and more is provided by the desire of palladium to attain planarity than the urge for nickel or cobalt to do so. 

Other metal salts, such as Cr3+, Rh3+ or Ru3+ derivatives, catalyze the cyclization of dihydrobilin to porphyrin [63] differently from copper, these metals afford the metal-free ligand and this seems to be a suitable route for the preparation of porphyrins with acid-labile substituents, which in the previous method suffer during the removal of the copper atom. On the other hand, dihydrobilin also cyclizes to porphyrin when heated in 1,2-dichlorobenzene or when treated with bases although in lower yields [3, 8, 10]. The presence of nickel or cobalt salts seems to be necessary to drive the cyclization reaction towards the formation of the octadehydrocorrin structure. 

The last two examples strongly suggest the possibility that these cyclization reactions proceed through bis(allyl)nickel intermediates,1 particularly since... 

Nickel catalysts for the syntheses of cyclic compounds were first successfully utilized by Reppe, who was able to prepare cyclooctatetraene from acetylene (65). This eight-membered ring synthesis, and also the preparation of cyclic products from strained olefins (e.g., bicycloheptene and norbornadiene) and acrylonitrile, have been adequately reviewed elsewhere (7) and will therefore not be considered further. A short account of the cyclization reactions of butadiene using nickel-containing catalysts has appeared previously in this series (/). The discovery of new synthetic possibilities and a deeper understanding of the mechanism of these reactions justify a more extensive treatment. 

Formation of the DVCB derivatives is complicated by the nickel-catalyzed isomerization of m-piperylene into traw.v-piperylene which proceeds through the formation of the cyclobutane (LIII). The rate of isomerization is dependent on the nature of the ligand attached to the metal, and increases in the series tri(o-phenylphenyl)phosphite < triphenyl-phosphine < tricyclohexylphosphine. In the case of the nickel-tricyclo-hexylphosphine catalyst, the rate of isomerization is faster than the cyclization reaction. 

Radical cyclization reactions can be carried out by treating an unsaturated alkyl iodide or bromide with Et2Zn in the presence of palladium(II) or nickel(II) complexes.28 Under these conditions, an intermediate Pd(0) or Ni(0) complex is formed which initiates a radical chain reaction providing a new cyclized zinc cyclopentylmethyl derivative which can be trapped with various electrophiles in the presence of a copper catalyst. A related cyclization can be... 

Benzenesulfenyl chloride can convm unsaturated adds to lactones. The unsatuiated add (7) is treated with benzenesulfenyl chloride, followed by Raney nickel, to afford the 7-lactone (8) in excdlent overall yield (equation 5). Another acid (9) has been lactonized to produce the spiro-p-lactone (10) whidi rearranges on silica gel to 7-lactone (11 equation 6). 6-Lactones have been also prqrared using diis rq>-proach. An additional advantage of this approach is that the phenyl sulfide moiety can be manipulated into a variety of functional groups to facilitate cyclization. in suirunary, successfiil cyclization reactions... 

The above concept of catalytic metallo-ene cyclizations (Scheme 36) may also be extended to platinum and nickel, as one would expect in view of previous work on intermolecular nickel-ene reactions (cf. Section 1.2.2.4). 

These reactions turned out to be preparatively very useful since they allow the performance of radical cyclization reactions but produce an organozinc halide as a final product (Scheme 9-33) [65-70]. The treatment of an unsaturated alkyl halide 36 (X = Br, I) with a palladium(O) or nickel(O) complex produces, via a one-electron transfer [72], a paramagnetic nickel(I) or palladium(I) salt MLj,(X) (M = Ni, Pd) and a radical 37 which undergoes a smooth cyclization reaction and produces, after recombination with the transition-metal moiety, the nickel(ll) or palladium(II) species 38. After transmetallation with a zinc(II) salt, a stable organozinc cyclopentylmethyl derivative of type 39 is produced. 

TJ ecent articles of this series (18) reported investigations of the synthe-sis of cyclododecatriene from butadiene (6) using a nickel catalyst. These investigations culminated in isolating a crystalline intermediate of this cyclization reaction (19). Strong support for the proposed structure of the intermediate, I was obtained by synthesizing bis (7r-allyl) nickel II (20). Subsequently, several 7r-allyl compounds of many transition metals were synthesized (21). 

Instead of a second or third alkyne, an alkene C=C double bond may be incorporated into the cyclotrimerization reaction. Iron [65], rhodium [66], nickel [67], palladium [68], or cobalt [69] catalysts have been used to form cyclohexa-dienes. However, the preparative use of this catalytic co-cyclization is disturbed by consecutive side reactions of the resulting dienes such as cycloaddition or dehydrogenation. Itoh, Ibers and co-workers [70] have reported the straight palladium-catalyzed co-cyclization reaction of C2(C02Me)2 and norbomene (eq. (24)). 

Carbon-carbon bond formation with electrogenerated nickel and palladium complexes in cyclization reactions leading to the formation of heterocycles 03EJ01605. 

Similar to the nickel-catalyzed reactions, metallacycles of palladium are assumed to be intermediates of these conversions. They were isolable in some cases. Thus, 3,3-dimethylcyclopropene with -allyl( ) -cyclopentadienyl)palladium, on cyclizing oxidative addition, formed metallacyclopentanes 20 and metallacyclononanes 21, depending on the reaction conditions. Thermal decomplexation via reductive elimination gave cyclopropane systems and products thereof. ... 

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