Ni-catalyzed reactions

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

This reaction exemplified that the regiochemistry of RS and H introduced by car-bonylahve addition differed from that of those by simple hydrothiolation. In the Rh-catalyzed hydrothiolation, the ArS group added to the terminal carbon and H to the internal carbon (Eq. 7.12). On the other hand, in the Rh-catalyzed thioformylation, RS was placed at internal carbon and formyl at the terminal carbon in spite of using the same catalyst precursor, [RhCljPPhsjs], which was also active for the thioformylation shown in Eq. (7.17). In 1997, the Pt-catalyzed hydrothiocarboxylation using RSH, alkyne and CO was reported to furnish 24 (Eq. 7.18), which showed the same regiochemistry as the Ni-catalyzed reaction shown in Eq. (7.1) [28]. 

Scheme 6/4.12. Four component Ni°-catalyzed reaction of alkynes, organometallics, enones and TMSCI.

Primary and secondary alkylzinc iodides and benzylic zinc halides also undergo Ni-catalyzed reactions with various primary alkyl iodides and bromides.407-409 According to the procedure by Knochel and co-workers, the transformations with alkylzinc iodides, which are less reactive than the corresponding dialkylzincs, require the presence of two additives Bu4NI and 4-fluorostyrene (Scheme 155).407,408... 

One of the most recent developments in the field of Ni-catalyzed reactions of alkyl halides with organozinc derivatives is a study of Terao et al.411 They reported the use of three additives in the couplings 1,3-butadiene, N,N-bis(penta-2,4-dienyl)benzylamine 308a, and 2,2-bis(penta-2,4-dienyl)malonic acid dimethyl ester 308b. Addition of tetraene 308b to the reaction mixtures significantly increased the product yields (Scheme 157). The remarkable effect of these additives was explained by the formation of the bis-7r-allylic complex 309 as the key intermediate (Scheme 158). 

Sato et al. <1997JA6984> (Scheme 48, Equation 15) and Tang and Montgomery <2000JA6950> (Scheme 48, Equation 16) attached the alkynyl substituent on nitrogen inducing the cyclization of the intermediate 225 by a Ti- or Ni-catalyzed reaction, respectively. 

Apart from the electrocarbonylation reactions of organic halides described in Sect. 6, other Ni-catalyzed reactions leading to ketones have been reported. Thus the electroreductive coupling between acylchlorides and alkyl halides, catalyzed by NiBr2bpy leads to unsymmetrical ketones [129]. Recently acylchlorides have been converted to symmetrical ketones in an undivided cell fitted with a nickel or stainless steel anode. In this reaction the active metallic species... 

Chlorobenzene reacts with alkenes with bimetallic catalyses of Ni and Pd. Chlorobenzene is converted in situ into iodobenzene (14) by the Ni-catalyzed reaction of Nal at 140 ,C. NiBr , rather than the Ni(0) complex, is found to be a good catalyst. Then the Pd-catalyzed reaction of the iodobenzene with acrylate takes placef 15],... 

SCHEME 27. Effects of a proximal -bond in the Ni-catalyzed reaction of Et2Zn with alkyl... 

Although not discussed in this chapter, the Tsuji-Trost reaction159 is undoubtedly the most extensively investigated Pd-catalyzed allylation with allyl electrophiles. There have also been some uncatalyzed and Cu-catalyzed reactions of allyl electrophiles with alkyl metals and metal cyanides. On the other hand, the Pd- or Ni-catalyzed reactions of allyl electrophiles with organometals containing allyl-, benzyl-, propargyl- and other alkylmetals do not appear to have been extensively investigated. 

In the original investigation of the Pd- or Ni-catalyzed alkenyl-benzyl and benzyl-alkenyl coupling reactions168, both Pd- and Ni-phosphine catalysts were shown to be effective. In some Ni-catalyzed reactions, however, double-bond migration to produce styrene derivatives was observed as a side reaction169. Nonetheless, both Pd- and Ni-catalyzed procedures have been successfully applied to the synthesis of various coenzymes Q , where n is < 10, and related menaquinones (Scheme 63)171,172. 

Following a report in 1992 on the reaction of /3-hydrogen-containing alkyl iodides with alkyl-, aryl- and alkenyl-9-BBN derivatives in the presence of Pd(PPh3)4 and K3PO4208, Knochel and coworkers made an interesting and potentially important observation on the effect of proximal -bonds shown in Scheme 2790. This may have paved the way to their subsequent discovery of the Ni-catalyzed reaction of alkylzincs with primary alkyl iodides in the presence of an electron-deficient styrene or acetophenone90,91 (Scheme 74)... 

SCHEME 73. Ni-catalyzed reaction of Grignard reagents or organozincs with neopentyl-type iodides... 

SCHEME 74. Ni-catalyzed reaction of organozincs with primary alkyl iodides promoted by electron-deficient styrenes or acetophenone... 

SCHEME 79. Ni-catalyzed reaction of primary alkylzincs with secondary alkyl bromides... 

A few interesting variants of the Pd-catalyzed acylation of organozincs have been developed. In one such variant, thiol esters are employed in place of acyl chlorides214. Another is the Ni-catalyzed reaction of organozincs with cyclic anhydrides215 shown in Scheme 82. this desymmetrization reaction can be made highly enantioselective, it would become a significant tool for asymmetric synthesis. 

The angular methyl group is introduced by a Ni-catalyzed reaction. 

A comparable study of the Ni-catalyzed reactions of isobutene, 1-butene, and cis-butene-2 in the presence of H2 and D2 has revealed a very complex series of chemical reactions that take place, including induced isomerization of 1-butene to 2-butene, deuterium exchange, induced cis-trans isomerization of butene-2, and finally, addition to the double bond. Below 200 mm Hg pressure, the rates of exchange, addition, and isomerization are about equal for 1-butene and are about % order in olefin and order in H2. With increasing excess of H2 this approaches zero order in olefin and % order in H2, while for large excess of 1-butene, all reactions become inhibited (30 to 150°C). Although the authors have attempted to discuss mechanisms in connection with the data, the lack of information on the isotherms makes that of dubious value. 

The Ni-catalyzed reaction of ( )-l-aIkenylalanes and ( )-l-alkenylzirconium derivatives with aryl halides (ArX) gave the corresponding cross-coupled products in good yields, as shown in Table 5.1. 

In a similar manner, the Pd- or Ni-catalyzed reaction of ( )-l-alkenylalanes with alkenyl halides gave the corresponding dienes with high stereoisomeric purity (Scheme 5.24). 

It was later demonstrated that both Ni and Pd° species catalyzed the conversion of l-methyl-2-vinyl-3-prop-2-enylcyclobutanes to ( )-3,7-di-ethylcycloocta-1,5-diene. However, as shown in Scheme 4, [PdCl2(PhCN)2] forms an equal quantity of the (Z)-isomer, the sole product of the thermal rearrangement. A side reaction in the Ni -catalyzed reaction clearly demonstrates the scission of the C-C bond required in the rearrangement, by producing penta-1,3-diene in low yield. 

Cross-coupling reactions with allylic halides are especially high-yield reactions. They occur with high S 2 selectivity, in contrast to the corresponding Pd " - or Ni -catalyzed reactions which give the S ,j2 product (Scheme 9-18) [44-46]. 

The Pd- or Ni-catalyzed reaction of tiialkylsilylmethylmetals containing Zn or Mg provides a novel regio- and stereo-controlled route to allylsilanes [82-84] (Scheme 1-26). Another useful application of Pd-catalyzed alkylation is the / -substitution reaction of zinc homoenolates [85-89] (Scheme 1-27) and higher homologues [90]. 

In the case of tetramethylbutatriene, Ni(0) catalyzes not only the cyclodimerization (formation of [4]radialene 94), but also the cyclotrimerization, leading to [6]radialene 95 and its isomer 96 (see also Section ILD). The product pattern depends to some extent on the nature of the catalyst, but the choice of solvent seems to be more crucial. This is illustrated impressively by the Ni(cod)2-catalyzed reaction of 93, which leads exclusively to the [4]radialene in toluene solution, but to the [6]radialene in DMF. Interestingly, the stoichiometric reaction between 93 and (2,2Tbipyridyl)-(l,5-cyclooctadiene)nickel yields the nickel complex 97, which has been isolated and characterized by X-ray diffraction. On treatment of 97 with two equivalents of maleic anhydride, reductive elimination of nickel takes place and octamethyl[4]radialene (94) is formed in good yield. This reaction sequence sheds light on the mechanism of the Ni-catalyzed reactions mentioned above further ideas on the mechanism of the cyclodimerization and cyclotrimerization reactions have been developed by lyoda and coworkers. ... 

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