Palladium alkynes

Balme G, Bouyssi D, Monteiro N (2002) Palladium-Catalyed Reactions Involving Attack on Palladium-Alkene, Palladium-Alkyne, and Related jr-Complexes by Carbon Nucleophiles. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 2245... 

IR spectroscopy can aid in the identification of some Pd-C gronps. Palladium acyls generally have a strong absorption between 1630 and 1720 cm. a-bonded palladium alkynes have an absorption band of variable intensity between 1950 and 2125 cm, and a-alkenes have vc=c between 1535 and 1630 cm . ... 

Balme, G., Bouyssi, D., Monteiro, N. Palladium-catalyzed reactions involving attack on palladium-alkene, palladium-alkyne, and related ic-complexes by carbon nucleophiles. Handbook of Organopattadium Chemistry for Organic Synthesis 2002, 2, 2245-2265. 

P. M. Henry, Palladium-Catalyzed Reactions Involving Nucleophilic Attack on 7i-Ligands of Palladium-Alkene, Palladium-Alkyne, and Related Derivatives, in Handbook of Organopalladium Chemistry for Organic Synthesis, E.-i. Negishi, Ed., Wiley-Interscience New York, 2002, pp. 2119-2139. 

Alkyne cross-coupling reactions over the last 25 years have become one of the most valuable assets in the synthetic chemist s toolbox. The now famous Sonogashira coupling (50, 114) of terminal alkynes with aryl or vinyl halides is readily achieved with a palladium catalyst, a copper(l) cocatalyst, and amine base. In the catalytic cycle (Scheme 14a), copper-and palladium-alkyne complexes are the key intermediates that lead to coupling of R and R units via the alkyne. Analogously, the Stille coupling... 

V 3 Palladium-Catalyzed Reactions Involving Nucleophilic Attack on 7T-Ligands of Palladium-Alkene, Palladium-Alkyne, and Related Derivatives... 

Scheme 26.19 Relay 1,4 organocatalytic addition/palladium alkyne addition processes.

Complexation of triynes to Pd(0) has been reported to give homoleptic palladium alkyne complexes that show a trigonal-planar arrangement with all of the alkyne carbons and Pd in the same plane. Complex 73 is a macrocyclic complex synthesized by reaction of the triyne with Pd(PPh3)4- Due to coordination to the metal, the alkyne carbons are shifted to the center of the cycle and their substituents deviate from linearity by about 22°. Complex 74 undergoes clean intramolecular cyclization at room temperature upon addition of PPh3 (Equation (24)). No intermediate complexes were detected in the course of this reaction, which is an example of the important cycloisomerization of alkynes and enynes catalyzed, among other transition metal complexes, by Pd(0) derivatives. 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

The conditions for hydrogenation of alkynes are similar to those employed for alkenes In the presence of finely divided platinum palladium nickel or rhodium two molar equivalents of hydrogen add to the triple bond of an alkyne to yield an alkane... 

Hydrogenation of alkynes may be halted at the alkene stage by using special catalysts Lindlar palladium is the metal catalyst employed most often Hydrogenation occurs with syn stereochemistry and yields a cis alkene... 

Lindlar catalyst (Section 9 9) A catalyst for the hydrogenation of alkynes to as alkenes It is composed of palladium which has been poisoned with lead(II) acetate and quino line supported on calcium carbonate... 

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). 

Closely related to the Heck reaction is the Sonogashira reaction i.e. the palladium-catalyzed cross-coupling of a vinyl or aryl halide 20 and a terminal alkyne 21 ... 

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 ... 

Alkynes can be reduced to yield alkenes and alkanes. Complete reduction of the triple bond over a palladium hydrogenation catalyst yields an alkane partial reduction by catalytic hydrogenation over a Lindlar catalyst yields a cis alkene. Reduction of (he alkyne with lithium in ammonia yields a trans alkene. 

A synthetically useful virtue of enol triflates is that they are amenable to palladium-catalyzed carbon-carbon bond-forming reactions under mild conditions. When a solution of enol triflate 21 and tetrakis(triphenylphosphine)palladium(o) in benzene is treated with a mixture of terminal alkyne 17, n-propylamine, and cuprous iodide,17 intermediate 22 is formed in 76-84% yield. Although a partial hydrogenation of the alkyne in 22 could conceivably secure the formation of the cis C1-C2 olefin, a chemoselective hydrobora-tion/protonation sequence was found to be a much more reliable and suitable alternative. Thus, sequential hydroboration of the alkyne 22 with dicyclohexylborane, protonolysis, oxidative workup, and hydrolysis of the oxabicyclo[2.2.2]octyl ester protecting group gives dienic carboxylic acid 15 in a yield of 86% from 22. 

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