Alkynes palladium complexes

Alkenyl zirconium complexes derived from alkynes form C—C bonds when added to aHyUc palladium complexes. The stereochemistry differs from that found in reactions of corresponding carbanions with aHyl—Pd in a way that suggests the Cp2ZrRCl alkylates first at Pd, rather than by direct attack on the aUyl group (259). 

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

It was found [99JCS(PI )3713] that, in all cases, the formation of the deiodinated products 38 and 39 was accompanied by formation of the diynes 40 which were isolated in 60-90% yield. The authors believed that the mechanism of deiodination may be represented as an interaction ofbis(triphenylphosphine)phenylethynyl-palladium(II) hydride with the 4-iodopyrazole, giving rise to the bisftriphenylphos-phine)phenylethynyl palladium(II) iodide complex which, due to the reductive elimination of 1 -iodoalkyne and subsequent addition of alk-1 -yne, converts into the initial palladium complex. Furthermore, the interaction of 1-iodoalkynes with the initial alkyne in the presence of Cul and EtsN (the Cadiot-Chodkiewicz reaction) results in the formation of the observed disubstituted butadiynes 40 (Scheme 51). 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

In the case of 3-alkynylamines, IH proceeds exclusively in a S-Endo-Dig process to give substituted 1-pyrrolines. The best catalysts are palladium complexes (Eq. 4.69) the reaction fails for terminal alkyne owing to the formation of a stable palladium acetylide [278]. 

NMR monitoring of the reaction of the palladium complex with 1-octyne suggested that the alkyne inserts into the Pd-H bond. Further heating produced a mixture of the two regioisomeric alkenylphosphine oxides, the anti-Markovnikov adduct being the favored product (54 46, 65% yield). 

The intramolecular addition of the O-H bond to alkynes catalyzed by palladium complexes has been developed by K. Utimoto et al. (Eq. 6.59) [104]. An alkynyl alcohol can be converted to a cyclic alkenyl ether in the presence of a catalytic amount of [PdCl2(PhCN)2 or [PdCl2(MeCN)2] in ether or THE at room temperature. When the reaction was carried out in MeCN-H20 under reflux in the presence of a catalytic amount of PdCl2, hydration of the acetylenic alcohol occurred and the ketoalcohol was obtained in good yield instead. 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

Palladium complexes are effective catalysts for the reductive cydization of enyne substrates [53,54], The first report of catalytic cydization of 1,6- and 1,7-enynes 115a,b to cyclopentane 116a and cyclohexane 116b derivatives appeared in 1987 (Eq. 19) [70]. The authors proposed that the Pd(II) species 117 forms by oxidative addition of acetic acid to Pd(0) (Scheme 25). Complex 117 hydrometallates the alkyne to give 118, which cyclizes to provide... 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

An aromatic C-H functionalization involving the m-addition of benzene to internal alkynes is mediated by a bimetallic palladium complex in the presence of catalytic amounts of a borane. The mechanism of process remains to be clarified (Equation (77)).73... 

The addition of terminal alkynes to allenylphosphine oxides is catalyzed by palladium complexes (Equation (194)).157... 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

Addition of diphenyl disulfide (PhS)2 to terminal alkynes is catalyzed by palladium complexes to give l,2-bis(phe-nylthio)alkenes (Table 3)168-172 The reaction is stereoselective, affording the (Z)-adducts as the major isomer. A rhodium(i) catalyst system works well for less reactive aliphatic disulfides.173 Bis(triisopropylsilyl) disulfide adds to alkynes to give (Z)-l,2-bis(silylsulfanyl)alkenes, which allows further transformations of the silyl group to occur with various electrophiles.174,175 Diphenyl diselenide also undergoes the 1,2-addition to terminal alkynes in the presence of palladium catalysts.176... 

The reactions catalyzed by cationic palladium complexes are believed to proceed via a different mechanism (Scheme 67).273 Initially, a cationic silylpalladium(n) species is generated by cr-bond metathesis of the Br-Pd+ with a silylstannane. Subsequently, the alkyne and alkene moieties of the 1,6-diyne successively insert into the Pd-Si bond to form a cationic alkylpalladium(n), which then undergoes bond metathesis with silylstannane to liberate the product and regenerate the active catalyst species, S/-Pd+. 

Substituting the benzene ring with a double bond, Pd-catalyzed intramolecular alkoxylation of alkyne 122 also proceeded via an alkenyl palladium complex to form furan 123 instead of a benzofurans [99, 100]. In addition, 3-hydroxyalkylbenzo[fc]furans was prepared by Bishop et al via a Pd-catalyzed heteroannulation of silyl-protected alkynols with 2-iodophenol in a fashion akin to the Larock indole synthesis, [101]. 

Terminal allenes.1 A synthesis of 1,2-dienes (3) from an aldehyde or a ketone involves addition of ethynylmagnesium bromide followed by reaction of the adduct with methyl chloroformate. The product, a 3-methoxycarbonyloxy-l-alkyne (2), can be reduced to an allene by transfer hydrogenolysis with ammonium formate catalyzed by a zero-valent palladium complex of 1 and a trialkylphosphine. The choice of solvent is also important. Best results are obtained with THF at 20-30° or with DMF at 70°. 

In conjunction with this, Jeong reported the cycloadditions of bis(allyl) and bis(homoallyl) acetals of alkynals leading to bicyclic lactols. Smaltz extended its utility to the synthesis of carbocyclic nucleoside by coupling with nucleophilic substitution of a 7r-allylic palladium complex (Equation (46)). ... 

Yamamoto has proposed a mechanism for the palladium-catalyzed cyclization/hydrosilylation of enynes that accounts for the selective delivery of the silane to the more substituted C=C bond. Initial conversion of [(77 -C3H5)Pd(GOD)] [PF6] to a cationic palladium hydride species followed by complexation of the diyne could form the cationic diynylpalladium hydride intermediate Ib (Scheme 2). Hydrometallation of the less-substituted alkyne would form the palladium alkenyl alkyne complex Ilb that could undergo intramolecular carbometallation to form the palladium dienyl complex Illb. Silylative cleavage of the Pd-G bond, perhaps via cr-bond metathesis, would then release the silylated diene with regeneration of a palladium hydride species (Scheme 2). 

A similar addition to alkynes results in the formation of the corresponding unsaturated acids and derivatives.14,23,121-124 Cobalt, nickel, and iron carbonyls, as well as palladium complexes, are the most often used catalysts.14... 

Highly selective transformation of terminal acetylenes to either linear or branched carboxylic acids or esters may be achieved by appropriately selected catalyst systems. Branched esters are formed with high selectivity when the acetylenes are reacted with 1-butanol by the catalyst system Pd(dba)2/PPh3/TsOH (dba = dibenzylideneacetone) or palladium complexes containing PPh3. Pd(acac)2 in combination with various N- and O-containing phosphines and methanesulfonic acid is also an efficient catalyst for the alkoxycarbonylation of 1-alkynes to yield the branched product with almost complete selectivity.307,308... 

Catalytic systems to afford linear esters selectively are scant.306,309 A report in 1995 disclosed that palladium complexes based on l,l -bis(diphenylphosphine)fer-rocene showed excellent regioselectivity for the formation of linear a,p-unsaturated esters.309 The results with phenylacetylene are remarkable because this compound is known to exhibit a distinct preference for the formation of the branched products on palladium-catalyzed carboxylations. Mechanistic studies indicate that the alkoxycarbonylation of alkynes proceeds via the protonation of a Pd(0)-alkyne species to give a Pd-vinyl complex, followed by CO insertion and alcoholysis.310... 

Pyrrole and indole rings can also be constructed by intramolecular addition of nitrogen to a multiple bond activated by metal ion complexation. Thus, 1-aminomethyl-l-alkynyl carbinols (obtained by reduction of cyanohydrins of acetylenic ketones) are cyclized to pyrroles by palladium(II) salts. In this reaction the palladium(II)-complexed alkyne functions as the electrophile with aromatization involving elimination of palladium(II) and water (Scheme 42) (81TL4277). 

Though platinum and its complexes induce the polymerization of silacyclobutanes, palladium complexes catalyze the insertion of alkynes into the silacyclobutane ring. This reaction is very clean and provides a useful synthetic route to silacyclohexenes (Scheme... 

---