Hydration of unsaturated carbon compounds is one of the most straightforward and environmentally benign methods to form the carbon±oxygen bond. Synthesis of carbonyl compounds by the hydration of alkynes is an important variation in this category, which has been extensively studied. [1] Acidcatalyzed hydration of alkynes is long known. [2, 3] However, only electron-rich acetylene compounds, such as alkynyl ethers, alkynyl thioethers and ynamines react satisfactorily. [1d, 4] The reaction of simple alkynes is usually sluggish and needs cocatalysts, typically toxic mercury(ii) salts, to enhance the reactivity. [5] More recent interest lies in the use of transition-metal-complex catalysts containing Ru II , [6] Ru III , [7] Rh, [8] Pt, [9] Au III , [10] and other metal centers. [11] However, the process catalyzed by these complexes is not efficient either. The highest turnover frequency (TOF) is 550 h À1 claimed as the initial TOF for the hydration of 3-pentyn-1-ol catalyzed by [cis-PtCl 2 (tppts) 2 ] (tppts ¼ P(m-C 6 H 4 SO 3 Na) 3 ), but its overall TOF is no more than approximately 100 h À1 . [9c] Recently Teles and co-workers reported the addition of methanol to alkynes catalyzed by Au I species in conjunction with acidic cocatalysts. [12] Hydration of propargyl alcohol was also briefly mentioned in their patent application, [13] although the yield was quite low. [14] Herein we report that the Au I ±acid systems in aqueous methanol serve as powerful catalysts, [15] which promote the hydration of alkynes [Eq. (1)] and have turnover frequencies of at least two orders of magnitude higher than [cis-PtCl 2 (tppts) 2 ].In a preliminary experiment, a mixture of 1-octyne (1 mmol), [(Ph 3 P)AuCH 3 ] (0.01 mmol, 1 mol %) and concentrated sulfuric acid (0.5 mmol, 50 mol %) in aqueous methanol (1.5 mL, methanol:H 2 O ¼ 2:1 v/v) was heated for 1 h at 70 8C affording the corresponding Markovnikov hydration product, 2-octanone, in 95 % yield without anti-Markovnikov hydration, or possible methanol addition. [12] The reaction did not proceed in the absence of either the Au catalyst or sulfuric acid.The following aspects about the catalytic system are worth noting. First, the nature of the reaction medium significantly affects the reaction. The reaction run without using solvent (in otherwise the same conditions as the preliminary experiment) did not furnish 2-octanone. On the other hand, the use of 2propanol (71 %), dioxane (56 %), acetonitrile (53 %), or THF (11 %) resulted in a low yield, and the yield obtained with dichloromethane, DMF, or toluene was even lower. Thus methanol was the solvent of choice for this particular transformation. [16] Second, the efficiency of the catalyst was significantly enhanced by addition of appropriate ligands, which enabled the quantity of the precious catalyst used to be minimized. For instance, the control experiment run without ligand addition under the conditions shown in Table 1 (only 0.01 mol % catalyst) gave 2-octanone in only 35 % yield (TOF ¼ 3500 h À1 , entry 1), while th...
[reaction: see text] Addition of aniline derivatives to aromatic and aliphatic alkynes proceeds efficiently in the presence of a gold(I) catalyst (0.01-1.0 mol %) to afford ketimines in good yields
When RuH2(CO)(PPh3)3 was reacted with 2,2-dimethyl-1-(2-p-tolylphenyl)propan-1-one (2), the ruthenium-aryloxy complex 3 was obtained in 76% yield. The structure of this complex was determined from 1H and 31P NMR and X-ray data. Complex 3 showed the catalytic activity for the coupling of 2 with the phenylboronate 4. The 1H and 31P NMR studies of the reaction of Ru(CO)(PPh3)3 with o-aryloxy pivalophenone revealed that the C-H bond cleavage is a kinetically favorable process but the C-O bond cleavage is a thermodynamic one. The reaction of 2'-methoxyacetophenone with vinylsilane and organoboronate resulted in chemoselective C-C bond formation.
Ruthenium-catalyzed silylation of sp3 C-H bonds at a benzylic position with hydrosilanes gave benzylsilanes. For this silylation reaction, Ru3(CO)12 complex showed high catalytic activity. This silylation proceeded at the methyl C-H bond selectively. For this silylation reaction, pyridyl and pyrazolyl groups, and the imino group in hydrazones, can function as a directing group. Several hydrosilanes involving triethyl-, dimethylphenyl-, tert-butyldimethyl-, and triphenylsilanes can be used as a silylating reagent. Coordination of an sp2 nitrogen atom to the ruthenium complex is important for achieving this silylation reaction.
Ruthenium-catalyzed regioselective direct amino- and alkoxycarbonylations of aromatic rings via C-H bond cleavage using chlorocarbonyl compounds are described. A broad generality of amide and ester groups was achieved taking advantage of the wide availability of carbonylating agents. Alkyl chloroformates, inapplicable to usual Friedel-Crafts methods, can also be used for direct catalytic alkoxycarbonylation.
Mechanistic studies of the ruthenium-catalyzed reaction of aromatic ketones with olefins are presented. Treatment of the original catalyst, RuH(2)(CO)(PPh(3))(3), with trimethylvinylsilane at 90 °C for 1-1.5 h afforded an activated ruthenium catalyst, Ru(o-C(6)H(4)PPh(2))(H)(CO)(PPh(3))(2), as a mixture of four geometric isomers. The activated complex showed high catalytic activity for C-H/olefin coupling, and the reaction of 2'-methylacetophenone with trimethylvinylsilane at room temperature for 48 h gave the corresponding ortho-alkylation product in 99% isolated yield. The activated catalyst was thermally robust and showed excellent catalytic activity under refluxing toluene conditions. (1)H and (31)P NMR studies of the C-H/olefin coupling at room temperature suggested that an ortho-ruthenated complex, P,P'-cis-C,H-cis-Ru(2'-(6'-MeC(6)H(4)C(O)Me))(H)(CO)(PPh(3))(2), participated in the reaction as a key intermediate. Isotope labeling studies using acetophenone-d(5) indicated that the rate-limiting step was the C-C bond formation, not the C-H bond cleavage, and that each step prior to the reductive elimination was reversible. The rate of C-H/olefin coupling was found to exhibit pseudo first-order kinetics and to show first-order dependence on the ruthenium complex concentration.
Palladium-catalysed carbonylation of aryl halides with alcohols or NEt 2 H proceeds in ionic liquid media (1-butyl-3-methylimidazolium tetrafluoroborate or hexafluorophosphate). The catalyst/ionic liquid mixture could be recycled, after separation of the product by either distillation or extraction with ether. Carbonylation with alcohols forming benzoates was greatly accelerated by the use of ionic liquid.
Hydration of unsaturated carbon compounds is one of the most straightforward and environmentally benign methods to form the carbon±oxygen bond. Synthesis of carbonyl compounds by the hydration of alkynes is an important variation in this category, which has been extensively studied. [1] Acidcatalyzed hydration of alkynes is long known. [2, 3] However, only electron-rich acetylene compounds, such as alkynyl ethers, alkynyl thioethers and ynamines react satisfactorily. [1d, 4] The reaction of simple alkynes is usually sluggish and needs cocatalysts, typically toxic mercury(ii) salts, to enhance the reactivity. [5] More recent interest lies in the use of transition-metal-complex catalysts containing Ru II , [6] Ru III , [7] Rh, [8] Pt, [9] Au III , [10] and other metal centers. [11] However, the process catalyzed by these complexes is not efficient either. The highest turnover frequency (TOF) is 550 h À1 claimed as the initial TOF for the hydration of 3-pentyn-1-ol catalyzed by [cis-PtCl 2 (tppts) 2 ] (tppts ¼ P(m-C 6 H 4 SO 3 Na) 3 ), but its overall TOF is no more than approximately 100 h À1 . [9c] Recently Teles and co-workers reported the addition of methanol to alkynes catalyzed by Au I species in conjunction with acidic cocatalysts. [12] Hydration of propargyl alcohol was also briefly mentioned in their patent application, [13] although the yield was quite low. [14] Herein we report that the Au I ±acid systems in aqueous methanol serve as powerful catalysts, [15] which promote the hydration of alkynes [Eq. (1)] and have turnover frequencies of at least two orders of magnitude higher than [cis-PtCl 2 (tppts) 2 ].In a preliminary experiment, a mixture of 1-octyne (1 mmol), [(Ph 3 P)AuCH 3 ] (0.01 mmol, 1 mol %) and concentrated sulfuric acid (0.5 mmol, 50 mol %) in aqueous methanol (1.5 mL, methanol:H 2 O ¼ 2:1 v/v) was heated for 1 h at 70 8C affording the corresponding Markovnikov hydration product, 2-octanone, in 95 % yield without anti-Markovnikov hydration, or possible methanol addition. [12] The reaction did not proceed in the absence of either the Au catalyst or sulfuric acid.The following aspects about the catalytic system are worth noting. First, the nature of the reaction medium significantly affects the reaction. The reaction run without using solvent (in otherwise the same conditions as the preliminary experiment) did not furnish 2-octanone. On the other hand, the use of 2propanol (71 %), dioxane (56 %), acetonitrile (53 %), or THF (11 %) resulted in a low yield, and the yield obtained with dichloromethane, DMF, or toluene was even lower. Thus methanol was the solvent of choice for this particular transformation. [16] Second, the efficiency of the catalyst was significantly enhanced by addition of appropriate ligands, which enabled the quantity of the precious catalyst used to be minimized. For instance, the control experiment run without ligand addition under the conditions shown in Table 1 (only 0.01 mol % catalyst) gave 2-octanone in only 35 % yield (TOF ¼ 3500 h À1 , entry 1), while th...
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