Acetylene complexes acylation

Terminal alkyne anions are popular reagents for the acyl anion synthons (RCHjCO"). If this nucleophile is added to aldehydes or ketones, the triple bond remains. This can be con verted to an alkynemercury(II) complex with mercuric salts and is hydrated with water or acids to form ketones (M.M.T. Khan, 1974). The more substituted carbon atom of the al-kynes is converted preferentially into a carbonyl group. Highly substituted a-hydroxyketones are available by this method (J.A. Katzenellenbogen, 1973). Acetylene itself can react with two molecules of an aldehyde or a ketone (V. jager, 1977). Hydration then leads to 1,4-dihydroxy-2-butanones. The 1,4-diols tend to condense to tetrahydrofuran derivatives in the presence of acids. 

In principle, the acylation of aliphatic compounds is analogous with the Friedel-Crafts acylation of aromatics in the sense that a hydrogen of the reacting alkanes, alkenes, or alkynes is replaced by an acyl group to yield ketones, unsaturated ketones, or conjugated acetylenic ketones, respectively. As discussed subsequently, however, the reactions are more complex. The acylation of aliphatics is an important but less frequently used and studied process.11-13... 

Clean formation of a, p-acetylenic ketones could be achieved by carrying out the reaction with a catalytic amount of Cul in the presence of Et3N [Eq. (8.17)]124 or inducing the acylation with a Pd complex and Cul in the presence of Et2NH 125... 

A cationic acetylene carbene complex has been prepared by alkylation of an acyl oxygen (77). The alkyne ligand remains intact and retains the spectral properties of a four-electron donor on conversion of the neutral acyl to the cationic heteroatom carbene [Eq. (25)]. Mayr has entered... 

Upon addition of Me0(0)CsC(0)0Me (DMAD) to a solution of 4 a third type of reactivity was observed. In contrast to the situation with the isonitriles described above, the acetylene readily inserted into the Pt-acyl bond to afford the alkenyl complex 8 [17]. 

The reaction occurs well below the temperature at which most of the parent metal carbonyls exchange with free CO and so is a direct nucleophilic attack on coordinated CO, although it may alternatively proceed via a prior electron path. The resulting acyl anions can be isolated as their [R4N] " or [ (C6H5)3P 2N] salts but are reactive and are used directly in subsequent alkylations with organic halides, acetylenes, a-/i-unsaturated carbonyls and alkyloxonium salts to form organic condensation products or metal-carbene complexes. 

Representative reactions with (jt-C3H5)Ru(CO)3X are as follows. Alkynes, such as acetylene, phenylacetylene, and diphenylacetylene, react with (jr-C3H5)Ru(CO)3Cl at 60-90 °C in aromatic hydrocarbons to give acyl complexes with a formula of... 

The complex- imns-RhCI(CO)(PPh3)2 has recently been show-n to act as a catalyst for the hydroformylation of olefins and acetylenes under mild conditions, and for decarbonylation of aldehydes and of acyl and aroyl halides. ... 

Similar reactions have been carried out on acetylene.In an interesting variation, thiocarbonates add to aUcynes in the presence of a palladium catalyst to give a p-phenylthio a,p-unsaturated ester.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 cyclopentanone with a rhodium-complex catalyst. An intramolecular acyl addition to an alkyne was reported using silyl ketones, acetic aid and a rhodium catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. 

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

To investigate the oxidative addition of acyl halides to a metal to form the acyl complex and to find a better decarbonylation agent, we selected chlorotris(triphenylphosphine) rhodium (XI) as a model complex. This complex is known to catalyze the oxo reaction (8) and the homogeneous hydrogenation of acetylenes and olefins (7, 28). 

Moreover, aryl-oxazoles, -imidazoles [17], or-thiazoles [18], anhydrides [19], and imides [20] are accessible via intramolecular Heck-type carbonylations. In addition to typical acid derivatives, aldehydes [21], ketones [22], aroyl cyanides, aroyl acetylenes, and their derivatives [23] could be synthesized via nucleophilic attack of the acyl metal complex with the corresponding hydrogen or carbon nucleophiles. Even anionic metal complexes like [Co(CO)4] can act as nucleophiles and lead to aroylcobalt complexes as products [24]. 

The transition metals and their salts and coordination complexes such as RhCla, Pd(PPh3)4, Pd(OAc)2, Cu(0), CuCl and CuX2 can catalyze the aryl-aryl coupling, carbonylation and phenylation reactions of organobismuth compounds with indoles, acyl chlorides, acetylenes and olefins, as illustrated in Table 5.12. Most of these reactions proceed under mild conditions. 

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