Alkynyl aryl iodide

To date, only double Heck reactions have been described, but triple Heck reactions are also possible [39]. Reaction of the alkynyl aryl iodide 6/1-55 with norbor-nene in the presence of Pd(OAc)2, triphenylphosphane and triethylamine as base led to the cyclopropanated norbornene derivate 6/1-59 as a single diastereomer in 40% yield (Scheme 6/1.13). It can be assumed that the alkenyl Pd-species 6/1-56 is first formed stereoselectively, and this undergoes a Heck reaction with norbornene... 

In another interesting example by Grigg and Sridharan [45], the reaction of the alkynyl aryl iodide 71 with norbomene in the presence of Pd(OAc)2, triphenylphosphine and triethylamine led to the cyclopropanated norbomene derivate 75 as a single diasteieomer in 40% yield. It can be assumed that, first, the alkenyl palladium species 72 is formed stereoselectively, which undergoes a Mizoroki-Heck reaction with norbomene to give 73 in a jy -fashion followed by formation of the cyclopropanated intermediate 74, which loses HPdl (Scheme 8.17). 

The carbonylation of aryl iodides in the presence of terminal alkynes affords the acyl alkynes 565. Bidentate ligands such as dppf give good results. When PhjP is used, phenylacetylene is converted into diphenylacetylene as a main product[4l5]. Triflates react similarly to give the alkynyl ketones 566[4I6], In... 

Copper iodide acts as an efficient reagent for the nucleophilic displacement of 1-haloalkynes. It transforms 1-bromoalkynes (72) into 1-iodoalkynes (73) which, on further treatment with copper(II) bis(arenesulfinate), are converted into the corresponding alkynyl aryl sulfones (74). An electron transfer between 1-haloalkynes and copper(I) salts is believed to take place for the copper-assisted halogen-exchange reaction at the acetylenic carbon atom. 

As noted for the Heck reaction, aryl, alkenyl, and alkynyl bromides, iodides, and triflates are best for the oxidative addition. However, aromatic, heteroaromatic, alkenyl, and even alkyl boronic acids and esters can be coupled effectively. The reaction appears almost oblivious to other functional groups present ... 

The alkyne insertion reaction is terminated by anion capture. As examples of the termination by the anion capture, the alkenylpalladium intermediate 189, formed by the intramolecular insertion of 188, is terminated by hydrogenolysis with formic acid to give the terminal alkene 192. Palladium formate 190 is formed, and decarboxylated to give the hydridopalladium 191, reductive elimination of which gives the alkene 192 [81]. Similarly the intramolecular insertion of 193 is terminated by transmetallation of 194 with the tin acetylide 195 (or alkynyl anion capture) to give the dienyne 196 [82], Various heterocyclic compounds are prepared by heteroannulation using aryl iodides 68 and 69, and internal alkynes. Although the mechanism is not clear, alkenylpalladiums, formed by insertion of alkynes, are trapped by nucleophiles... 

The carbonylation of aryl iodide in the presence of terminal alkynes affords acyl alkynes. Bidentate ligands such as DPPF give good results [241]. When PI13P is used, phenylacetylene is mainly converted to diphenylacetylene. The alkynyl ketones 488 are prepared by the reaction of the alkenyl triflate 487 with phenylacetylene and CO [242],... 

Scheme 5.34 shows the transformations used for the synthesis of dendritic wedges (147) that are functionalized with aryl iodide and trimethylsilyl protected arylalkyne moieties at the focal region. Reaction of 3,5-dibromobenzotriazene (148) with one equivalent of isopropoxy-protected acetylene 149, followed by treatment with base, gave the 3-bromo-5-ethynylaryltriazene (150). Higher selectivity of Pd-catalyzed alkynylation of aryl iodides (e.g., 146) afforded the difunctionalized wedge (151). 

All of the neutral (organo-)copper compounds just listed can be arylated by aryl iodides and/or -bromides Ar-Cu and R-C=C-Cu can also be alkynylated by alkynyl iodides and/or -bromides. Table 16.2 summarizes the whole spectrum of corresponding products. After having grasped the mechanism of these reactions by way of Figure 16.3, we will discuss their synthetic potential by means of the examples given in Figures 16.4-16.9. 

With the aid of a fluoride ion source, alkynyltrimethylsilanes work as effective alkynyl donors in the Pd-catalyzed cross-coupling with alkenyl iodides.43,43a Recent studies have revealed that the alkynylsilanes react smoothly with aryl iodides and triflates, alkenyl triflates, or alkynyl chlorides under co-catalysis by a Cu or Ag salt.45 46a The use of a Pd/imidazolium chloride system in the presence of Cs2CC>3 and a Cu co-catalyst enables an efficient coupling between alkynyltrimethylsilanes and aryl bromides.47 In some cases, this catalytic system works well under Cu-free conditions. Alkynylsilanols also can be used as alkynyl donors in the coupling with aryl iodides.48 49 When TBAF is employed as activator, the coupling proceeds efficiently without co-catalyst.48... 

Alkynylsilanes can be converted into alkynylcoppers by treatment with Cu salts in an aprotic polar solvent such as l,3-dimethyl-2-imidazolidinone (DMI).62 The Cu-promoted coupling reactions via the Si-Cu transmetallation of alkynylsilanes are valuable for the syntheses of alkynyl ketones, 1,3-diynes, 1,3-enynes, and 1-aryl-l-alkynes from acid chlorides,62 alkynyl chlorides,63 alkenyl iodides,64 and aryl iodides,64 respectively (Equation (12)). In addition, symmetric 1,3-diynes can be prepared by the CuCl-mediated homocoupling of alkynylsilanes.65 653... 

R2X = RCOCI, alkynyl chlorides, alkenyl and aryl iodides... 

The same authors also reported on palladium-catalyzed domino cycli-zation-anion capture reactions employing allene (69) as a relay switch (Scheme 10) [52], Such a reaction of the alkynyl-tethered aryl iodide 68 starts with an oxidative addition to the catalytic metal species, and is followed by an intramolecular carbopalladation of the triple bond. An intermolecular car-... 

In the following scheme, the benzo[Z>]furan core of antibiotic erypoegin H was built up by a PtCL-catalyzed cycloisomerization of or// o-alkynylphenyl-0,(9-acetals <07AGE4760>. A similar type of reaction was applied to the syntheses of 2,3-disubstituted bcnzo b furans <07T8670>. A metal-catalyzed cyclization was also used in the syntheses of 5,6-disubstituted furo 2,3-c/]pyrimidines from alkynyl-pyrimidinols and aryl iodides <07T1931>. 

After carbonylative alkynylation of aryl iodides 34 with terminal alkynes 4 and in the presence of carbon monoxide under ambient pressure the subsequent addition of an amidinium salt 32 gives rise to the formation of 2,4,6-trisubstituted pyrimidines 33 in the sense of a four-component reaction (Scheme 25) [143]. 

Glyoxylative-decarbonylative alkynylations proceed considerably faster than carbonylative alkynylations of (hetero)aryl iodides with carbon monoxide and a lower catalyst loading is needed [143]. The mild conditions for decarbonylations are unprecedented, and the reagents are applied only in equimolar quantities with a high tolerance for various substiments. In addition, the application of alkynones 37, 45, and 46 in a subsequent transformation into heteroaryl 2-amino pyrimidines also illustrates the vast potential to diversity-oriented syntheses of heterocycles. 

The original procedure involved the coupling of aryl bromides with secondary amines. However, since then the scope has been expanded to include substrates such as aryl iodides, chlorides, fluorides, triflates, tosylates, nonaflates, iodonium salts, and even boronic acids. While the reaction has not been extensively utilized with vinyl or alkynyl substrates, it can be performed with various heteroaryl halides. Similarly, numerous types of nitrogen-containing coupling partners, including primary amines, imines, various azoles, lactams, and simple amides, can now be used in this reaction. 

Allyl hahdes, aryl iodides (alkynyl iodides)," iodine, and alkynes react with zirconacycles by replacing the C-Zr bond(s) stereoselectively. In the presence of CuCl the (Z,Z)-1,4-dicupriobutadienes may be the intermediates. The last process has imphcations in the cyclotrimerization of alkynes hy Cp2ZtCl2. 

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