Coupling with alkenyl halides

As shown in Eq. 2.39, 1,1-dihaloalkenes react with zirconacyclopentadienes to afford fulvene compounds (56) [7p]. 

After treatment of zirconacyclopentadienes with 2 equivalents of CuCl at room temperature, the addition of a halogenating agent such as NBS at —78 °C leads to the formation of octatetraenes 57a [7m]. This reaction involves slow bromination of the diene-dicopper compounds and coupling with the alkenyl bromide moiety (Eq. 2.40). 

A more direct coupling affording an eight-membered ring is that of bicyclic zirconacyclopentadienes with diiododienes. As shown in Eq. 2.41 [36a], in the presence of the standard 2.1 equivalents of CuCl and 3 equivalents of DMPU, bicyclic zirconacyclopentadienes react with bicyclic diiododienes to produce similar eight-membered ring compounds. This 

Preparation of a tricyclic cyclooctatetraene from a bicyclic zirconacyclopentadiene and a diiododiene. 

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Another type of copper reagent was prepared from RZnI/CuCN, and this was shown to couple with alkenyl halides." ... 

Alkenylboronic acids, alkenyl boronate esters, and alkenylboranes can be coupled with alkenyl halides by palladium catalysts to give dienes.223... 

Dienes. 4 (Z)-Dialkenyl cuprates couple with alkenyl halides in the presence of Pd[P(C6H5)j]4 to form conjugated dienes in good yield, but with fair stereoselectivity. If 1 equivalent of zinc bromide (8, 86) is present, the configuration of the alkenyl halide is retained ( 99.5%). 

Alkynyl(trimethyl)silanes smoothly couple with alkenyl halides at room temperature in the presence of a palladium catalyst and TASF (Eq. 5) [4]. The difference in reactivity between alkynylstannanes and -silanes were utilized in a palladium-catalyzed three component cross-coupling reaction. Thus, the palladium-catalyzed sequential reaction of tributylstannyl(trimethylsilyl)ethyne... 

Heterosubstituted 1,3-dienes. Some alkenylmetals substituted by OR, SR, or SiR, can be coupled with alkenyl halides (or aryl halides) in the presence of this Pd(0) catalyst. Alkenylzinc reagents, prepared by reaction of alkenyllithiums with ZnCh, and alkenyl-alanes are the most useful. Yields from reactions with organoboronates are low. 

In the same manner that various alkenylboron species can be coupled with alkenyl halides, so too can aryl halides be homologated to styrenes (Scheme 26). - In general, such reactions require a Pd catalyst and the presence of a base, such as sodium ethoxide, in order to achieve this type of head to head coupling. In sharp contrast, mainly head to tail products are formed when a weak base, such as triethyl-... 

Alkenylation. Grignard reagents or organozinc halides couple with alkenyl halides with Co(acac)2 as catalyst. The configuration of the double bond is retained. 

Other couplings. 1-Alkylthio-l,3-butadienes are assembled by a one-pot method involving hydroboration of thioalkynes and Suzuki coupling with alkenyl halides, both reactions catalyzed by Pd(II). Ullmann coupling using a Cu-(PhjPjjPdCh/DMSO system delivers nitrophenylpyridines. ... 

Dienes. The (E)-l-alkcnylzirconium compounds, obtained by hydrozirconation of 1-alkynes (6, 177-178), undergo cross coupling with alkenyl halides to form conjugated dienes (cf. the similar reaction of alkcnylalanes with alkenyl halides, 7, 95-96). In the present synthesis tetrakis(triphenylphosphine)-palladium (6, 571-573) can usually serve as catalyst. Nickel catalysts are less effective than Pd catalysts in this case. ... 

Alkynyl(trimethyl)silanes smoothly couple with alkenyl halides at room temperature in the presence of a palladium catalyst and TASF (Scheme The difference in... 

Scheme 1.14 Iron-catalyzed cross-coupling with alkenyl halide 39 (Kochi, 1971).

Haloboration of 1-aIkynes followed by chemoselective cross-coupling can provide j8,/3-substituted alkenylborons that undergo Pd-catalyzed coupling with alkenyl halides to give stereodeflned trisubstituted alkenes. The use of other /3,/3-substituted alkenyl-metals has also been demonstrated. For example, exocyclic alkenylmetals containing Zn and Sn have been nsed in Pd-catalyzed cross-coupling approach to the vitamin D skeleton as shown in Scheme 65. It shonld be noted that the alkenylzinc appeared to be distinctly snperior to the corresponding alkenyltins. 

Recently, Krasovskiy and Lipshutz thoroughly investigated the influence of ligands in the Negishi coupling with alkenyl halides. ... 

Lewis acid and source of nucleophilic ethyl groups, couples with alkenyl halides in the presence of a transition metal catalyst "" selective hydrocyanation agent in combination with HCN")... 

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