Alkynes palladium catalyst

The increase of selectivity in consecutive reactions in favor of the intermediate product may be sometimes extraordinarily high. Thus, for example, in the already cited hydrogenation of acetylene on a platinum and a palladium catalyst (45, 46) or in the hydrogenation or deuteration of 2-butynes on a palladium catalyst (57, 58), high selectivities in favor of reaction intermediates (alkenes) are obtained, even though their hydrogenation is in itself faster than the hydrogenation of alkynes. 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Thiols add to alkenes under photochemical conditions to form thioethers, and the reaction can be done intramolecularly to give cyclic thioethers. Thiols also add to alkynes and with a palladium catalyst, vinyl sulfides can be formed. " Selenium compounds (RSeH) add in a similar manner. ... 

The reaction can be done intramolecularly. N-Benzyl pent-4-ynamide reacted with tetrabutylammonium fluoride to an alkylidene lactam. Similar addition of a tosylamide-alkene, with a palladium catalyst, led to a vinyl Al-tosyl pyrrolidine. Similar cyclization reactions occur with tosylamide-alkynes. ... 

Imides can also add to alkenes or alkynes. Ethyl 2-propynoate reacted with phthalimide, in the presence of a palladium catalyst, to give ethyl 2-phthalimido-2-propenoate. ... 

Alkenes and alkynes can also add to each other to give cyclic products in other ways (see 15-61 and 15-63). The first exclusive exo-dig carbocyclization was reported using HfCU as a catalyst. Alkynes also add to alkenes for form rings in the presence of a palladium catalyst or a zirconium catalyst. " Carbocyclization of an alkene unit to another alkene unit was reported using an yttrium catalyst and alkenes add to alkynes to give cyclic compounds with titanium catalysts. ... 

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

Similar reactions have been carried out on acetylene. Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones. In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopen-tanone with a rhodium-complex catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. ... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

Hydroboration of alkenes or alkynes followed by cross-coupling with organic electrophiles provides a straightforward method for the carbon-carbon bond formation (Scheme 1-19). The hydroboration of thioalkynes with catecholborane in the presence of a nickel or palladium catalyst yields P-(aLkylthio)-l-alkenylboronates (72a)... 

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... 

The synthesis of (5 5 5) fused heterocyclic compounds 7 <2001JOC412> has been achieved in 84% yield via annulation of internal alkynes by imines 287 derived from o-iodoaniline in the presence of palladium catalyst (Scheme 51). 

In the presence of copper and palladium catalysts, terminal alkynes 1222 react with trimethylsilyl azide and allyl methyl carbonate to provide 2,4-disubstituted 1,2,3-triazoles 1223 in moderate to good yield. Isomerization of the allyl substituent in the presence of a ruthenium catalyst gives 4-substituted 2-(l-propen-l-yl)-2//-l,2,3-triazoles 1224. 

Benzyne, which is generated in situ from 2-(trimethylsilyl)phenyl triflate and KF, acts as an alkyne congener in distannation in the presence of palladium-/ r/-alkyl isocyanide complex.157 A variety of substituted benzyne derivatives inserts into the Sn-Sn bond to give l,2-bis(stannyl)benzenes (Equation (59)). The reaction fails to occur in the presence of other palladium catalysts such as Pd(PPh3)4. 

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 reaction mechanism was considered to be oxidative cyclization, and pal-ladacyclopentene 32 was formed. Reductive elimination then occurs to give cyclobutene 33, whose bond isomerization occurs to give diene 28. The insertion of alkyne (DMAD) into the carbon palladium bond of 32 followed by reductive elimination occurs to give [2+2+2] cocyclization product 27. Although the results of the reactions of E- and Z-isomers of 29 with palladium catalyst 26a were accommodated by this pathway, Trost considered the possibility of migration of substituents. Therefore, 13C-labeled substrate 25 13C was used for this reaction. 

A development of the last two decades is the use of Wacker activation for intramolecular attack of nucleophiles to alkenes in the synthesis of organic molecules [9], In most examples, the nucleophilic attack is intramolecular, as the rates of intermolecular reactions are very low. The reaction has been applied in a large variety of organic syntheses and is usually referred to as Wacker (type) activation of alkene (or alkynes). If oxygen is the nucleophile, it is called oxypalladation [10], Figure 15.4 shows an example. During these reactions the palladium catalyst is often also a good isomerisation catalyst, which leads to the formation of several isomers. 

Another interesting example involves the dihydrosilylation of alkynes [20], which is carried out at room temperature in two steps, the first one with platinum chloride (0.01%) and the second one with palladium-MOP catalysts (0.3%). The reaction can be done with solely the palladium catalyst, but in that case the yield for the first step is low. The work-up leads to the formation of a chiral diol in high optical yield when the MOP derivative shown is used (Figure 18.12). 

Alkynes may also be hydrogenated, initially to alkenes, and then further to alkanes. By suitable modification of the catalyst, it has proved possible to stop the reaction at the intermediate alkene. Typically, platinum or palladium catalysts partially deactivated (poisoned) with lead salts are fonnd to be suitable for reduction of alkynes to alkenes. Again, syn addition is observed. 

Halogen atoms. The introduction of side-chains on 9-trifluoromethyl-paullone 409 can be accomplished applying a Stille coupling (Scheme 86, Section 5.2.1.1 (2005EJM655)). Similarly, a Heck reaction of iodo 409 with terminal alkenes under standard conditions affords 2-substituted paullones 413 exclusively as E-isomers. The reaction of terminal alkynes with 409 in the presence of cuprous iodide and a palladium catalyst in triethylamine furnishes the 2-alkynyl-paullones 412 (2000BMCL567). 

Hydrogen undergoes catalytic hydrogenation adding to unsaturated hydrocarbons, such as alkenes and alkynes forming alkanes. The reaction is catalyzed by nickel, platinum or palladium catalysts at ambient temperature. Hydrogenation of benzene over platinum catalyst yields cyclohexane, C6H12. 

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