Vinyl halides, cross-coupling with

In common with vinyl and aryl halides, it has now been shown that allenic and propargylic halides cross-couple with Grignard reagents in the presence of palladium catalysts. The product consists predominantly of the substituted allene... 

The cis thioboration of terminal alkynes with 9-(arylthio)-9-BBN is catalyzed by Pd(Pli3P)4 in the presence of styrene. The product 136 is converted into the vinyl sulfides 137 and 138 by the treatment with MeOH or by Pd-catalyzed cross-coupling with aryl or alkenyl halides using K3PO4 in DMF[68]. No thioboration takes place with internal alkynes. 

Because the vinylzinc and vinylcadmium reagents can be prepared directly from the vinyl halides (I, Br) with zinc or cadmium metal, this route avoids cross coupling processes and provides a one-pot in situ preparation of perfluo-rovinylcopper compounds Table 7 shows examples of this method of preparation of vinylcopper reagents from the indicated cadmium or zinc reagent [145]... 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Trapping experiments with electron deficient olefins such as acrylonitrile and 3-buten-2-one gave the expected 1,4-adducts from the proposed acylnickel intermediates. This provides strong support for the proposed mechanism. It was also demonstrated that allylic, vinylic and pentafluorophenyl halides could be cross-coupled with acid chlorides to give the corresponding ketones in good yields. 

Vinylic halides or vinyl-metal species couple with a very high degree of stereospecificity, cry-vinylic halides giving cis coupling products and tra/iy-vinylic halides trans coupling products (example 17, Table III). Aromatic halides give homo- or cross-coupling reactions (examples 18 and 19, Table III). 

A complementary approach for cross-couplings with allenes was applied by using metallated allene species instead of allenyl halides, which have already been discussed in Sect. 14.2.1. Since allenyllithium compounds are readily available by deprotonation of allenes with n-butyllithium, successful cross-coupling reactions between lithiated allenes such as 54 or 57 and aryl or vinylic halides allowed convenient routes to aryl- and vinyl-substituted allenes, e.g. 55, 58 and 60 (Scheme 14.15) [30],... 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

Alkyl halides other than aryl and vinyl halides do not readily undergo oxidative addition with Pd and must, in general, first be converted to alkylmetals. In this connection, however, a recent report on the Ni catalysed selective alkyl-alkyl cross-coupling with Ni(acac)2 and Lil in THF represents a significant breakthrough.34 In cases where the alkyl group contains a p-H atom, reduction of the organic halide via p-dehydropalladation reductive elimination can be a serious side-reaction (Scheme 11.6). 

New reports of organozirconium-organic halide cross-coupling reactions have almost completely stopped. Nevertheless, the palladium-catalyzed cross-coupling of vinyl zir-conocenes (from alkyne hydrozirconation) with vinyl halides has been employed in the synthesis of the lipid isobutylamide natural product anacyclin (equation 98). ... 

Most recently, Fu and co-workers [126] have reported that the use of Pd2(dba)3/PtBu3 as a catalyst for a wide range of aryl and vinyl halides, including chlorides, facilitates their Suzuki cross-coupling with arylboronic acids, giving the coupled products in very good yield, typi-... 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

Hydroxymethylation of organic halides can bt effected by metal-catalyzed cross-coupling with the Grignard reagent (diisopropoxymcthylsilyl)methylmagnesium chloride (1) followed by oxidation. This two-step process i- particularly useful for regio- and ster-eocontrolled conversion of vinyl halides into al.ylic alcohols and of allylic halides into homoallylic alcohols. ... 

By extension to cross-coupling with vinyl and aryl triflates, the scope of the Stille reaction has been expanded greatly. Almost all functional groups are tolerated without the need for protection. The reactivity order of organic halides is I>Br>OTf>>Cl, but the order between Br and OTf can be reversed by addition of LiCl. By addition of LiCl (2 or 3 equiv) to provide a more reactive Pd-intermediate (vinyl-PdCIl versus vinyl-PdOTfL ) [25] and/or stable tin by-product (RjSnCl versus R3SnOTf), the reaction proceeds smoothly at ambient temperature. 

Recently, the sequential, one-pot Pd-catalyzed coupling of an o-halophenol and a terminal alkyne, followed by cross-coupling with a vinylic halide has provided an efficient approach to a complex benzofuran-containing natural product (Eq.6) [27]. 

Arylboronic and alkenylboronic acids undergo transition metal complex-catalyzed synthetic organic reactions such as cross-coupling with organic halides [58-60], 1,4-addition to a,/I-unsaturated ketones [61-63], and ring-opening addition to vinyl oxirane [64]. Scheme 5.8 depicts the mechanism proposed for the... 

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