Alkynes catalytic oxidative carbonylation

Particularly significant results have been obtained in the oxidative carbonylation of simple and functionalized alkynes. Thus, the PdI2/KI-catalyzed oxidative carbonylation of simple alkyl- or arylacetylenes, as well as of propy-nyl alcohol and propynyl acetate, carried out in alcoholic solvents under mild conditions (15-25 atm of CO, 4-9 atm of air, 25-80 °C), led to the formation of maleic derivatives (together with small amounts of fumaric derivatives) and 5,5-dialkoxyfuran-2(5H)-ones, in high yields and with unprecedented catalytic efficiencies for this kind of reaction (up to ca. 4000 mol of product... 

By use of stoichiometric quantities of CuCl2, again in presence of a catalytic amount of PdCl2, an oxidative carbonylation of alkynes to the corresponding esters has been achieved.540 Sodium acetate was used as base. In its absence the reactions were no longer clean. The function of CuCl2 and NaOAc is indicated in equations (132)-(134). 

Suzuki and colleagues described the first palladium-catalyzed oxidative carbonylation of alkenylboranes as early as 1981. They prepared 1-alkenylboranes by hydroboration of alkynes and subsequent oxidative carbonylation mediated by a catalytic amount of PdCL, in the presence of NaOAc and BQ in methanol, which provided unsaturated esters in good yields (Scheme 8.27a) [106]. Later, a stereoselective synthesis of ]S-mono- and / , / -disubstituted a, ]S-unsaturated esters was established by a stepwise cross-coupling alkylation followed by an oxidative carbonylation of 2-bromo-1-alkenylboranes (Scheme 8.27b) [107]. Good yield and excellent stereoselectivity was achieved. 

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... 

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. 

Among the carbonylative cycloaddition reactions, the Pauson-Khand (P-K) reaction, in which an alkyne, an alkene, and carbon monoxide are condensed in a formal [2+2+1] cycloaddition to form cyclopentenones, has attracted considerable attention [3]. Significant progress in this reaction has been made in this decade. In the past, a stoichiometric amount of Co2(CO)8 was used as the source of CO. Various additive promoters, such as amines, amine N-oxides, phosphanes, ethers, and sulfides, have been developed thus far for a stoichiometric P-K reaction to proceed under milder reaction conditions. Other transition-metal carbonyl complexes, such as Fe(CO)4(acetone), W(CO)5(tetrahydrofuran), W(CO)5F, Cp2Mo2(CO)4, where Cp is cyclopentadienyl, and Mo(CO)6, are also used as the source of CO in place of Co2(CO)8. There has been significant interest in developing catalytic variants of the P-K reaction. Rautenstrauch et al. [4] reported the first catalytic P-K reaction in which alkenes are limited to reactive alkenes, such as ethylene and norbornene. Since 1994 when Jeong et al. [5] reported the first catalytic intramolecular P-K reaction, most attention has been focused on the modification of the cobalt catalytic system [3]. Recently, other transition-metal complexes, such as Ti [6], Rh [7], and Ir complexes [8], have been found to be active for intramolecular P-K reactions. 

At the same time, Reppe (158) discovered the catalytic properties of tetracarbonyinickel and its derivatives in the carbonylation reactions and in the cyclization of alkynes, and this gave a tremendous thrust forward to the experimental research on the chemistry of carbonylnickel derivatives. In the beginning the development of the chemistry of low oxidation states proceeded concomitantly with the chemistry of zerovalent... 

Parallel to the development of catalysts for olefin metathesis, the first alkyne metathesis catalysts were W and Mo metal oxides or carbonyls suspended on alumina or silica.65 The first homogeneous catalysts were developed by Mortreux and consisted of a mixture of Mo(CO)6 and substituted phenols.66 It was not until the work of Schrock and his collaborators, however, that a well-defined, isolable alkylidyne catalyst (38) was synthesized, characterized, and shown to catalyze alkyne metathesis.67 Later modifications on 38 included substituting the alkoxy groups with fluorinated analogs, and for the corresponding Mo alkylidynes (39), the fluorinated alkoxy groups are essential for catalytic activity.68... 

Muniz and co-workers prepared a series of substituted indoles (e.g., 76) using a modified Koser reagent that was made from iodosobenzene and 2,4,5-tris-isopropylbenzene sulfonic acid (77, TIPBSA). The hypervalent iodine reagent was used either stoichiometrically or in catalytic amounts with mCPBA as the terminal oxidant. A variety of N-protecting groups were tolerated and substituents on the aryl ring of 75 include halogens, carbonyls (aldehydes, ketones, esters), alkynes, and nitriles (HAG(I)7349). 

Cross-coupling of Ar(or vinyl)-X with organometaDic species, terminal alkynes, and olefins, as well as carbonylation in the presence of nucleophiles, represent well-known synthetic routes for C—C bond formation. As far as C-heteroatom bond formation is concerned, powerful synthetic procedures have been developed for selective formation of the C-P (P = R2P, R2P(0), R(R 0)P(0), (R0)2P(0)), C-SR, C SeR, C—NR2, and so on, bonds. All of these catalytic methods are based on substitution reactions. The catalytic cycle of a typical substitution reaction includes the following stages (i) oxidative addition, (ii) transmetaUation, and (iii) C-heter-oatom reductive elimination. 

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