Carbonylation of Internal Alkynes

Nickel-catalyzed carbonylation of a-haloalkynes with carbon monoxide under phase-transfer conditions gave either allenic monoacids or unsaturated diacids. The carbonylation initially afforded monoacids, which reacted further to give diacids with high stereoselectivity (Eq. 4.52). 

Nickel-catalyzed carbonylation of a-ketoalkynes has also been reported by Arzoumanian et al. under phase-transfer conditions. The carbonylation gave either furanone or unsaturated carboxylic acids depending on the substituents of substrates (Eq. 4.53). A similar reaction, nickel-catalyzed cyanation of a-ketoalkynes with KCN in water, was also reported to afford unsaturated hydroxylactams (Eq. 4.54).  

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). 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).  

Some time ago Takahashi and coworkers demonstrated that enynes could be converted into cyclic enones in a rhodium atalyzed hydroformylation [45] and in the course of these studies discovered that the use of water instead of hydrogen resulted in cyclocarbonylation to afford 2(5H)-furanones 51/52 (Equation 10.25). This reaction was subsequently applied to a range of internal alkynes to afford the 

Model stoichiometric reactions of [PdCH3(CO)(Pr DAB)] [B 3,5-(CF3)2C6H3 4] (Pr DAB = l,4-diisopropyl-l,4-diaza-l,3-butadiene) with alkynes and carbon monoxide have been investigated by NMR spectroscopy and DFT studies to identify the putative intermediates involved in the cydocarbonylation of alkynes [47]. Addition of but-2-yne (R = CH3) or 1-phenylpropyne (R= Ph) results in regioseledive insertion into the Pd-acyl bond to afford a five-membered palladacycle 54 that undergoes rapid cydocarbonylation at low temperature to afford a palladium-coordinated, q -allylic lactone 55. The a,f -unsaturated y-lactone could be liberated either by proton abstraction with a stoichiometric amount of Na[BEt3H] or by nucleophilic addition 

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Unsaturated lactones lacking substitution at C-4 are the simi est ones available via this general type of cycloaddition. Several syntheses of these lactones are of practical value, including two Pd-based meth-ods. However, the considerable utility of metal carbonyl anions in lactone synthesis is illustrated by a rhodium carbonyl anion catalyst system which gives very high yields upon reaction with a variety of internal alkynes under weakly basic aqueous conditions, essentially water-gas shift conditions. These conditions were established to maximize chemoselectivity with respect to other possible alkyne carbonylation products. Regioselectivity is modest in this process, but was not examined systematic ly (equation 13). ... 

A catalytic amount (5 mol%) of IrifJ, alters the ratio of 1,2- to 1,4-addition of Grignard reagents to a,/ -unsaturated carbonyl compounds [177]. In the presence of indium triflate or gallium chloride coupling of internal alkynes and aldehydes proceeds (Scheme 8.134) [178]. 

In a general illustration of the Dotz reaction a terminal or internal alkyne reacts with a carbene 123 and one carbonyl ligand at a [Cr(CO)3] template in a formal [3 + 2+1] cycloaddition reaction producing a chromium-complexed naphthol (124) under mild reaction conditions via the vinylketene intermediate 125 (see Scheme 57). Terminal alkynes (R1C = CR2 R HjR H) react with total regioselectivity, while the regiocontrol in the reaction course of internal alkynes... 

Rhodium-catalyzed ri.s carbocarbonylation of internal alkynes, under water-gas equilibrium conditions, selectively leads to 2(5/f)-furanones 36 30,31. In this case one of the two carbonyl groups is reduced to the alcohol, thus leading to the lactone. Similar examples with rhodium32 and palladium33 catalysts have been reported. 

In 2006, the group of Artok showed that 5-aryl-2(5H)-furanones could be prepared in moderate to good yields by a rhodium-catalyzed carbonylative arylation of internal alkynes with aryl boronic acids (Scheme 1.9a) [22]. a,P-Unsaturated ketones (chal-cone derivatives) were formed as the major product when some TFA (trifluoroacetic acid) was added under the same reaction conditions [23a]. By varying the catalytic system, indanones could be produced as the main product [23b]. The chemical behavior of terminal alkynes is different, and either a,P-unsaturated ketones or furans starting from propargylic alcohols can be achieved (Scheme 1.9b) [24, 25]. In the case of vinyl ketones, 1,4-diketones were obtained by rhodium-catalyzed coupling of arylboronic acids in the presence of 20-40 bar of CO [26]. In 2007, Chatani demonstrated that indenones could be accessed by a carbonylative rhodium-catalyzed cyclization of alkynes with 2-bromophenylboronic adds (Scheme 1.9c) [27]. Here, the key intermediate is a vinylrhodium(I) spedes that is formed by transmetaUation of RhCl with 2-bromophenylboronic acid followed by insertion of... 

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. 

Coperet, C., Sugihara, T., Wu, G., Shimoyama, 1. and Negishi, E. (1995) Acylpalladation of internal alkynes and palladium-catalyzed carbonylation of (Z)-P-iodoenones and related derivatives producing y-lactones and y-lactams. Journal if the American Chemical Society, 117, 3422-3431. 

Kadnikov, D.V. and Larock, R.C. (2000) Synthesis of coumarins via palladium-catalyzed carbonylative annulation of internal alkynes by o-iodophenols. Organic Letters, 2, 3643—3646. 

In the absence of nucleophilic solvents, (RC2H)Co2(Cp)6 compounds are carbonylated to produce butenolide complexes (XIV) in variable yields (Sternberg et al, 1959 Sauer et al, 1959 Mills and Robinson, 1967 Guthrie et al, 1975 Pdlyi et al, 1975). Complexes of internal alkynes generally fail to... 

Migration of a hydride ligand from Pd to a coordinated alkene (insertion of alkene) to form an alkyl ligand (alkylpalladium complex) (12) is a typical example of the a, /(-insertion of alkenes. In addition, many other un.saturated bonds such as in conjugated dienes, alkynes, CO2, and carbonyl groups, undergo the q, /(-insertion to Pd-X cr-bonds. The insertion of an internal alkyne to the Pd—C bond to form 13 can be understood as the c -carbopa-lladation of the alkyne. The insertion of butadiene into a Ph—Pd bond leads to the rr-allylpalladium complex 14. The insertion is usually highly stereospecific. 

Carbonylation of halides in the presence of terminal and internal alkynes produces a variety of products. The substituted indenone 564 is formed by the reaction of o-diiodobenzene. alkyne, and CO in the presence of Zn[414]. 

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. 

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