Propynes methoxycarbonylation

The discovery of the above-mentioned class of highly efficient alkyne carbonylation catalysts originated from a general study of reactions homogeneously catalyzed by cationic metal complexes [6, 8, 9], e. g., the methoxycarbonylation of propyne (eq. (2)). The catalysts applied were cationic palladium phosphine systems prepared in situ from three components (1) palladium acetate, (2) an excess (10-40-fold on Pd) of a (mono)phosphine ligand(L) and (3) an acid (HX) [8]. Methanol was used as both reactant and solvent, but many other solvents can also be used, such as A-methyl-2-pyrrolidone (NMP) or product MMA. 

In another group of (2 + 2)-cycloaddition reactions, the heterocyclic nucleus reacts via an electron-deficient carbon-carbon or carbon-nitrogen double bond with electron-rich aminoacetylenes (ynamines). For instance, thiete 1,1-dioxides, JV-benzylmaleimide, and 2,3-bis(methoxycarbonyl)-7-oxabicyclo( 2.2.1 lhepta-2,5-diene reacted with 1-diethylamino-l-propyne and with 1 -phenyl-2-( 1 -pyrrolidinyl)-acetylene to give the (2 + 2)-cycloadducts 48, 49, and 50, respec-tively.35,37,53 The latter product was thermally rather unstable, and its structure was identified on the basis of its conversion with 2,4,6-tri-methylbenzonitrile oxide into 51.53 (2 + 2)-Cycloaddition via a carbon-nitrogen double bond has been reported to take place in the reactions of 3,3-dimethyl-3//-indoles and 3,4-dihydroisoquinoline with ynamines, e.g., l-dimethylamino-2-phenylacetylene, in the presence of boron trifluoride.54 The (2 + 2)-cycloadducts 52 and 53 were not isolated, but... 

Another impressive ligand effect reported by Drent and coworkers [37] concerns the methoxycarbonylation of propyne to form methyl methacrylate. Triphenylphosphine modified palladium catalysts give low rates, but using 2-pyridyldiphenylphosphine instead gives very high rates and selectivities. The mechanism is still a matter of debate [38]. 

Production of this monomer amounts to 20 miUion tons/year. Traditionally, production was based on cheap and toxic raw materials acetone, a side product of the production of phenol, and hydrogen cyanide, which is highly toxic, a side product of the production of acrylonitrile. The process has now been abandoned because it produces 2.5 kg of ammonium hydrogen sulfate/kg of methyl methacrylate and is characterized by -factor 2.5. The catalytic process, introduced by chemists of the Shell Co., is based on the methoxycarbonylation of methy-lacetylene (propyne). Besides 100 % atom utihzation. this process is characterized by high chemical yield and selectivity, both over 99 % [12]. For the economy of any industrial process, the turnover is a particularly important technological parameter. Approximately 100,000 mols (ca. 4000 kg) of methylacetylene is... 

Formal insertion of CO2 into Fe-C bonds is formed in the reaction of Fe3(CO)i2 with hex-l-en-3-yne. The reaction consists in the splitting of water into its three components, favored by the tic silica used for purification. The final product is, however, a binuclear complex.Related to this behavior is the reaction of Fe3(CO)i2 with l-phenyl-2-propyn-l-ol where the allenylidene complex Fe3(GO)9(/x-GO) C=C=C(H)Ph 4 is obtained first. It reacts with methanol to form a ferrole-like methoxycarbonyl (or acetate) derivative. It has been also observed that similar binuclear complexes can be obtained by reacting Fe3(CO)i2 with propargyl alcohol or propargyl chloride in KOH/CH3OH solutions followed by acidification with HCl GO and methanol activation occurs in this instance to form binuclear methoxycarbonyl derivatives and the open cluster Fe3(GO)io H2GGG(H)G(=0)G[GH2(0)GH3GGH2] 5. ... 

---