The exclusive formation of cyclopentenones from molybdenum hexacarbonyl-catalyzed Pauson-Khand reactions of 5-allenyl-1-ynes

The exclusive formation of cyclopentenones (via path B) was observed in molybdenum hexacarbonyl (10 mol %) catalyzed Pauson-Khand reactions of 1,6-allenynes under 1 atm of CO (balloon) without any substitutent effect.     

The formation of cyclopentenones and 3(2h)-furanones from acetylenic precursors

Acetylenic alcohols, obtained in high yield from condensations of 3,3-diethoxypropyne or 3,3-ethylenedioxybutyne with cyclic ketones, may be used as substrates for cyclopentenone annelation or spirofuranone synthesis.     

Alpha-hydroxy cyclopentenones from alpha-diketones

[reaction: see text] Metalloenolates derived from alpha,beta-unsaturated alpha-diketones undergo cyclization to alpha-hydroxy cyclopentenones. This is apparently the first reported Nazarov reaction that takes place in the presence of base.     

Titanium-mediated [4 + 1] assembly of 1,3-dienes and nitriles: formation of 3-cyclopentenyl amines and cyclopentenones

In the presence of Ti(OiPr)4 and iPrMgCl, dienes couple with nitriles to afford the title products in good yields.     

Mechanism and kinetics of the hydrogenation of CO with the formation of paraffins and olefins on an iron catalyst

A kinetic model is proposed for the hydrogenation of CO on a Fe/Al₂O₃ catalyst, based on a mechanism of parallel formation of paraffins and olefins. The model satisfactorily describes the experimental data on the dependence of the total rate of conversion of CO to hydrocarbons and the selectivity with respect to paraffins on the composition of the reaction mixture. It was shown that in the case of olefins the successive steps of their hydrogenation, which make a substantial contribution to the distribution of reaction products, must be taken into consideration.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Nauki Prospekt, Kiev 252039, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 118–123, March–April, 1996. Original article submitted May 22, 1995.     

Oxygen harvesting from carbon dioxide: simultaneous epoxidation and CO formation

Due to increasing concentrations in the atmosphere, carbon dioxide has, in recent times, been targeted for utilisation (Carbon Capture Utilisation and Storage, CCUS). In particular, the production of CO from CO₂ has been an area of intense interest, particularly since the CO can be utilized in Fischer–Tropsch synthesis. Herein we report that CO₂ can also be used as a source of atomic oxygen that is efficiently harvested and used as a waste-free terminal oxidant for the oxidation of alkenes to epoxides. Simultaneously, the process yields CO. Utilization of the atomic oxygen does not only generate a valuable product, but also prevents the recombination of O and CO, thus increasing the yield of CO for possible application in the synthesis of higher-order hydrocarbons.

Selective formation of atomic oxygen to form epoxides in a waste free process is reported. Simultaneously generating carbon monoxide from carbon dioxide for further use.     

K/MgFeZn-HTLcs催化CO加氢制低碳烯烃性能研究

以MgFeZn-HTLcs为前驱体,制备了不同Mg/Fe/Zn物质的量配比、K改性的K/MgFeZn-HTLcs催化剂,用于CO加氢直接制低碳烯烃反应。采用N2吸附-脱附、SEM、TG、XRD、XPS、H_2-TPR等手段对催化剂进行了表征。结果表明,MgFeZnHTLcs前驱体具有典型的层状结构,孔径分布均一;经焙烧、K改性后仍具有一定的层状结构,但比表面积显著减小,平均孔径增大;新鲜催化剂物相以金属氧化物和铁酸盐为主,反应后K/MgFeZn-HTLcs催化剂主要以Fe_5C_2、MgCO_3和ZnO相存在,K/2Fe-1Zn催化剂主要物相为ZnFe2O_4。在CO加氢反应中,K/MgFeZn-HTLcs催化剂具有较高的C=2-4烯烃选择性和较低的C+5含量,与K/2Fe-1Zn催化剂相比,产物分布明显改善;K/2Mg-2Fe-1Zn催化剂上O/P比值达5.15,C=2-4含量占总烃质量的48.56%。     

Rh-catalyzed [5+1] and [4+1] cycloaddition reactions of 1,4-enyne esters with CO: a shortcut to functionalized resorcinols and cyclopentenones

We have developed novel Rh-catalyzed [n+1]-type cycloadditions of 1,4-enyne esters, which involve an acyloxy migration as a key step. The efficient preparation of functionalized resorcinols, including biaryl derivatives, from readily available 1,4-enyne esters and CO was achieved by Rh-catalyzed [5+1] cycloaddition accompanied by 1,2-acyloxy migration. When enyne esters had an internal alkyne moiety, the reaction proceeded by a [4+1]-type cycloaddition involving 1,3-acyloxy migration, leading to cyclopentenones.     

Hydrogenation promoting effect of iron on the catalytic properties of zirconium dioxide in the reaction of formation of light olefins from CO and H2

Iron admixtures (0.1 %) raise the activity of zirconium dioxide catalyst in regard to the formation of C₂-C₄ olefins from CO and H₂. Manifestation of the promoting effect in the synthesis of isobutylene (in contrast to C₂-C₃ olefins) requires close contact between the metal and ZrO₂. Iron promoted zirconium dioxide is more selective for olefins than is ZrO₂ with nickel admixtures.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 6, pp. 367–371, November December, 1996.     

An effective Pd-catalyzed hydroxycarbonylation of olefins with CO and HCOOH

A new protocol for Pd-catalyzed regioselective hydroxy-carbonylation of olefins with formic acid under low pressure of carbon monoxide has been developed. The same catalytic system provides good selectivity to 2-phenylpropionic acid in carbonylation of styrene and to linear acids in carbonylation of terminal alkenes. The reaction is highly susceptible to catalyst precursor and solvent nature.     

Novel 1:1 adducts from the reaction of hexafluoroacetone azine with various olefins and 1,3-dienes; Diels-Alder adducts as intermediates in the formation of criss-cross 2:1 adducts

Hexafluoroacetone azine¹ (I) has been reported^2,3 to react thermally (160–180°) with electron-rich olefins of type H₂CCHR (R  H, Me, or Et) to give “criss-cross” (1,3-:4,2-) adducts (II). In contrast, cis- or trans-but-2-ene and cyclohexene react under comparable conditions to give nitrogen and products derived formally from addition and insertion reactions of bis(trifluoromethyl)-carbene, although it is doubtful if the free carbene is involved^2,4. The reaction of azine (I) with alkanes is reported⁵ to involve a radical mechanism in which the diazo compound (CF₃)₂CN₂, and thence the carbene (CF₃)₂C:, is formed by a secondary process.     

Communication: New insight into the barrier governing CO2 formation from OH + CO

Despite its relative simplicity, the role of tunneling in the reaction OH + CO → H + CO(2) has eluded the quantitative predictive powers of theoretical reaction dynamics. In this study a one-dimensional effective barrier to the formation of H + CO(2) from the HOCO intermediate is directly extracted from dissociative photodetachment experiments on HOCO and DOCO. Comparison of this barrier to a computed minimum-energy barrier shows that tunneling deviates significantly from the calculated minimum-energy pathway, predicting product internal energy distributions that match those found in the experiment and tunneling lifetimes short enough to contribute significantly to the overall reaction. This barrier can be of direct use in kinetic and statistical models and aid in the further refinement of the potential energy surface and reaction dynamics calculations for this system.     

Unprecedented CO2-promoted aminochlorination of olefins with Chloramine-T

[STRUCTURE: SEE TEXT] A new synthetic procedure for the aminochlorination of olefins for the synthesis of vicinal chloroamine derivatives using a combination of Chloramine-T and carbon dioxide is described. The method can be applied to a variety of olefins, including an electron-sufficient olefin and a conjugated diene.     

Energetics of the biosynthesis of cyclopentenones from unsaturated fatty acids

Polyunsaturated fatty acids like linolenic acid or arachidonic acid upon enzymatic hydroxylation (lipoxygenases) can lead to corresponding hydroperoxides. Their dehydration gave rise to vinyl allene oxides, which cyclized into cyclopentenones, precursors of jasmonic acid or prostanoids.