Oxidative carbonylation of terminal alkynes

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

Later, a nickel-catalyzed cascade conversion of propargyl halides and propargyl alcohol into a pyrone in water was reported. The reaction involved a carbonylation by CO and a cyanation by KCN (Eq. 4.55).96 Recently, Gabriele et al. explored a facile synthesis of maleic acids by palladium catalyzed-oxidative carbonylation of terminal alkynes in aqueous DME (1,2-dimethoxyethane) (Eq. 4.56).97... 

Ishii and colleagues developed a multicatalytic system for the oxidative carbonylation of terminal alkynes [85]. In the presence of Pd(OAc)2, chlorohydro-quinone and NPMoV, under CO and O2, acetylenecarboxylate or phenylmaleic... 

Alkenes and alkynes can substitute for carbonyl ligands on Os3(CO)i2. Carbon monoxide slowly dissociates from Os3(CO)ii(j7 -PhC=CPh) and a cluster with a bridging alkyne ligand forms, Os3(CO)io(/n-PhC=CPh). The addition of ethene to the cluster gives a bridging vinylidene complex, Os3(CO)9(/u-H)2(/u-C=CH2). The oxidative addition of terminal alkynes to Os3(CO)i2 gives Os3(CO)9(/u.-H)(/u,3-CCR). Nucleophiles add to the bridging alkyne unit. 

Carbamates and ureas are easily prepared and separated from the oxidative carbonylation of amines catalyzed by [PdCl2(phenanthroline)] dissolved in [G4GiIm]BF4. The carbonylation of terminal 3-alkyn-l-ols and l-alkyn-4-ols by palladium acetate/2-(diphenylphosphino)pyridine dissolved in [G4CiIm]PF6 or [C4CiIm]BF4 affords quantitatively and selectively v< -a-methylene (Scheme 21) and 7- and -lactones, respectively. ... 

Oxidative carbonylation is another useful reaction. The following three types of oxidative carbonylation of alkynes are known. The first one is the synthesis of the acetylene carboxylates 299 via formation of the alkynylpalladium intermediate 298 from terminal alkynes (path a) [122]. 

The mild palladium(II)-copper(II)-CO-02-HQ system was also applied to the oxidative carbonylation of formate esters and olefins. Higher yields as well as branched/Iinear ester ratio were obtained by using excess rather than an equimolar quantity of formate ester to substrate. " In addition, allenes and terminal alkynes undergo regioseleclive hydroester-ification to unsaturated mono- and diesters using the same catalytic system. f ii... 

Unlike the cases of alkenes, Wacker-type intermolecular oxypalladation reactions of alkynes have not been extensively investigated, although their intramolecular cyclization reactions have been developed into synthetically useful procedures (Sects. V3.2). In principle, they can proceed by a few alternative paths shown for the cases of terminal alkynes in Scheme 14. In reality, however, alkynyl C—H activation by Pd to give alkynylpalladium derivatives shown in Scheme 3 may well be the dominant path, as suggested by the carbonylative oxidation of terminal alkynes to give alkynoic acid esters shown in Scheme 15. Oxidative dimerization of alkynes is a potentially serious side reaction. Further systematic investigation of this fundamentally important process appears to be highly desirable. 

A carbonyl compound will be the product of hydroboration-oxidation only if a second molecule of BH3 or R2BH does not add to the ir-bond of the boron-substituted alkene. In the case of internal alkynes, the substituents on the boron-substituted alkene prevent the approach of the second boron-containing molecule. In the case of terminal alkynes, however, there is an H instead of a bulky alkyl group on the carbon that the second molecule adds to, so there is less steric hindrance toward the second addition reaction. Therefore, either BH3 or R2BH can be used with internal alkenes, but the more sterically hindered R2BH should be used with terminal alkynes. 

Oxidative Carbonylation of Alkynes. The synthesis of acetylenecarboxylates is achieved using terminal acetylenes, aliphatic alcohols, and CO in the presence of PdBr2, CuBr2, and... 

Using a catalyst system of PdCl2, CuCH, HCl, and O2, the internal alkyne 20 is carbonylated at room temperature and 1 atm to give unsaturated esters[19]. This apparently oxidizing system leads to non-oxidative cu-hydroesterilica-tion. With terminal alkynes, however, oxidative carbonylation is observed. 

Substituted propargylamines 52 can be carbonylated in the presence of TsOH which may facilitate the oxidative addition of Pd(0) to the C-N bond to generate 53, and the 2,3-dienecarbamides 54 are obtained by CO insertion using DPPP as a ligand. The terminal alkynes 55 are converted to the 2,4-dienecarbamide 56 [14],... 

Addition of hydrosilane to alkenes, dienes and alkynes is called hydrosilylation, or hydrosilation, and is a commercially important process for the production of many organosilicon compounds. As related reactions, silylformylation of alkynes is treated in Section 7.1.2, and the reduction of carbonyl compounds to alcohols by hydrosilylation is treated in Section 10.2. Compared with other hydrometallations discussed so far, hydrosilylation is sluggish and proceeds satisfactorily only in the presence of catalysts [214], Chloroplatinic acid is the most active catalyst and the hydrosilylation of alkenes catalysed by E PtCU is operated commercially [215]. Colloidal Pt is said to be an active catalytic species. Even the internal alkenes 558 can be hydrosilylated in the presence of a Pt catalyst with concomitant isomerization of the double bond from an internal to a terminal position to give terminal silylalkanes 559. The oxidative addition of hydrosilane to form R Si—Pt—H 560 is the first step of the hydrosilylation, and insertion of alkenes to the Pt—H bond gives 561, and the alkylsilane 562 is obtained by reductive elimination. 

Oxidation of the vinylborane (using basic hydrogen peroxide) gives a vinyl alcohol (end), resulting from anti-Markovnikov addition of water across the triple bond. This end quickly tautomerizes to its more stable carbonyl (keto) form. In the case of a terminal alkyne, the keto product is an aldehyde. This sequence is an excellent method for converting terminal alkynes to aldehydes. 

Hydroboration-oxidation of an internal alkyne forms a ketone. Hydroboration of a terminal alkyne adds BH2 to the less substituted, terminal carbon. After oxidation to the enol, tautomerization yields an aldehyde, a carbonyl compound having a hydrogen atom bonded to the carbonyl carbon. 

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