Chan Sik Cho

Palladium-catalyzed cross-coupling of aryl and alkenyl boronic acids with alkenes via oxidative addition of a carbonboron bond to palladium(O)

Abstract Arylboronic acids react with alkenes in acetic acid at 25°C in the presence of a catalytic amount of palladium(II) acetate together with sodium acetate to give the corresponding aryl-substituted alkenes in high yields. Alkenylboronic acids react with alkenes under similar conditions to give the corresponding conjugated dienes stereospecifically, but the product yields are lower, compared with those from arylboronic acids. Similar treatment of sodium tetraphenylborate (NaBPh 4 ) with alkenes also affords the corresponding phenylated alkenes in high yields together with biphenyl and benzene as side products. Oxidative addition of a carbonboron bond to palladium(O), formed in situ , to give an organopalladium(II) species is assumed to be the key step of these cross-coupling reactions.

Sodium tetraphenylborate as a phenylating reagent in the palladium-catalyzed phenylation of alkenes and acid chlorides

Abstract Sodium tetraphenylborate (NaBPh 4 ) reacts with terminal alkenes in acetic acid at 25°C in the presence of a catalytic amount of palladium(II) acetate together with silver acetate as a re-oxidant to give the corresponding phenylated alkenes in 22–87% yield. It also reacts with acid chlorides in tetrahydrofuran (THF) at 25°C in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) to give the corresponding phenyl ketones in 51–100% yield. Carbonylation of the borate with 1–30 atm carbon monoxide (CO) in methanol at 25°C in the presence of palladium(II) acetate or sodium chloropalladate (Na 2 PdCl 4 ) affords a low yield (9–30%) of benzophenone and methyl benzoate, a higher pressure favoring the formation of the latter.

Palladium(II)-catalyzed phenylation of unsaturated compounds using phenylantimony chlorides under air ☆

Abstract Diphenylantimony chloride and phenylantimony dichloride, mainly the former, react smoothly with alkenes in acetonitrile at r.t. in the presence of a catalytic amount of Pd(OAc) 2 under air to afford the corresponding phenylated alkenes (Heck-type reaction). The addition of AgOAc as reoxidant is not necessary for this reaction in sharp contrast to similar reactions using triarylstibines. The oxygen absorption is confirmed in this catalytic reaction and the reaction does not proceed catalytically in palladium(II) under inert gases, such as nitrogen or argon. Even under air the addition of a radical scavenger stopped the reaction. The regeneration of PhPdOAc species from Ph 2 SbCl, HPdOAc species and oxygen is proposed as a key step in the catalytic cycle where oxygen-containing radical species might be present as intermediates.

Palladium-catalyzed cross-coupling reactions between organic tellurides and alkenes

Diaryl tellurides, alkenyl aryl tellurides and dialkenyl tellurides react efficiently with various alkenes in methanol in the presence of a catalytic amount of PdCl2 together with AgOAc and Et3N to give the corresponding aryl- and alkenyl-substituted alkenes with moderate to quantitative yields. Both monomeric and dimeric palladium complexes, (Ph2Te)2PdCl2 and [(Ph2Te)PdCl2]2 respectively, react readily with alkenes to give a high yield of phenyl-substituted alkenes. The key step of this coupling reaction is proposed to be the migration of an organic moiety from Te to Pd (transmetallation) in organic tellurine-PdCl2 complexes to afford organopalladium species.

Palladium(0)-catalyzed carbonylation of aryl and alkenyl boronic acids with carbon monoxide leading to esters and ketones. Transformation of a CB bond to a CCO bond

Abstract Arylboronic acids react with carbon monoxide (CO) at atmospheric pressure in methanol at 25°C in the presence of a catalytic amount (1–5 mol%) of tetrakis(triphenylphosphine)palladium(0) to give the corresponding methyl arenecarboxylates and diaryl ketones in moderate yield, where the addition of a base, especially sodium acetate, increases the selectivity for the esters. However, when the reactions are carried out in aprotic solvents such as tetrahydrofuran (THF), benzene, dichloromethane and dimethoxyethane, the ketones become the sole carbonylation products, THF being the solvent of choice. Alkenylboronic acids react similarly to afford selectively the corresponding methyl alkenecarboxylates in methanol and dialkenyl ketones in THF, respectively. A reaction pathway involving the oxidative addition of a carbon-boron bond to palladium(0) is proposed for this catalytic process.

Palladium-catalyzed homocoupling reactions of organic tellurides

Organic tellurides containing a styryl moiety react in acetonitrile to give the corresponding homocoupling products, 1,3-dienes, with moderate to quantitative yields in the presence of a catalytic amount of Pd(OAc)2 together with AgOAc at 25°C. In contrast, such homocoupling reactions hardly occur with diaryl, alkyl aryl, dialkyl, and alkynyl aryl tellurides, even at reflux temperature and in the presence of a stoichiometric amount of palladium salt, in disagreement with reported results. The result of cross-over experiments suggests that this homocoupling reaction occurs between an alkenyl telluride and an alkenylpalladium species, the latter being formed via the migration of an alkenyl moiety from Te to Pd (transmetallation).

Palladium(II)-catalyzed hydroarylation of α,β-unsaturated aldehydes and ketones with triarylstibines in the presence of silver acetate

Abstract Triarylstibines react with α,β-unsaturated aldehydes and ketones in acetic acid at 25°C in the presence of silver acetate and a catalytic amount of palladium(II) acetate to afford the hydroarylation products by conjugate addition in good yields.

Antimony(III) chloride as an efficient catalyst for palladium-catalyzed hydrophenylation of α,β-unsaturated ketones and aldehydes

Abstract A remarkable catalytic effect of antimony(III) chloride was disclosed in palladium-catalyzed hydrophenylation of α,β-unsaturated ketones and aldehydes (Michael-type conjugate addition) with sodium tetraphenylborate in acetic acid at 25°C.

Diacetoxylation of nonconjugated dienes with TeO2 and the isolation of intermediate organotellurium compounds

Abstract Tellurium(IV) oxide (TeO 2 ) reacts with nonconjugated dienes in acetic acid at reflux temperature in the presence of lithium halide or iodine to give the corresponding vic -diacetates in moderate yields. When the reaction is carried out at 80°C and the reaction mixture is then reduced with aqueous sodium thiosulfate, bis (β-acetoxyalkyl)ditellurides are isolated as main products. Treatment of the ditellurides with refluxing acetic acid affords the corresponding vic -diacetates in good yields. The expected tellurium containing heterocyclic compounds, such as telluracyclopentanes and telluracyclohexanes, are not formed and/or isolated under the conditions employed. When 4-vinylcyclohexene and limonene are used as dienes in the diacetoxylation reaction, aromatic compounds due to the dehydrogenation of cyclohexene ring are also produced in moderate yields.

The first example of carbonylation of triarylbismuthines : remarkable rhodium(I) catalysis

Triarylbismuthines (Ar3Bi: Ar = C6H5, 4-MeC6H4, 4-MeOC6H4, 4-ClC6H4) react with atmospheric pressure of carbon monoxide in acetonitrile, tetrahydrofuran or methanol at 25 °C in the presence of a catalytic amount of either [RhCl(CO)2]2 or RhCl3·3H2O to produce the corresponding diaryl ketones in good yields, methyl benzoates being also formed in methanol.