Reaction Of Allenes Research Articles

C3H3+ Isomers: Temperature Dependencies of Production in the H3+ Reaction with Allene and Loss by Dissociative Recombination with Electrons

A technique has been developed to simultaneously determine recombination rate coefficients, alpha e, and initial concentrations of ion types that coexist in a flowing afterglow plasma. This was tested using the H3(+) + allene reaction in which two different C3H3+ isomers are produced. Use of an electrostatic Langmuir probe enabled the C3H3+ isomer branching ratios for propargyl and cyclic C3H3+ from this allene reaction and their alpha e to be determined over the temperature range 172-489 K. The study showed that the cyclic C3H3+ to propargyl C3H3+ branching ratios from the allene reaction varied from 50/50 at 172 K to 18/82 at 489 K. Over this temperature range, the alpha e for both isomers change only slightly. The room temperature alpha e values for propargyl and cyclic C3H3+ are (1.15 +/- 0.2) x 10(-7) and (8.00 +/- 0.1) x 10(-7) cm3/s, respectively. The data are discussed relative to current theories and in relation to fuel-rich flame chemistry, interstellar molecular synthesis, and modeling of Titan's atmosphere.

Transition Metal-Catalyzed Intermolecular [5+2] and [5+2+1] Cycloadditions of Allenes and Vinylcyclopropanes

Initial examples of the intermolecular Rh(I)-catalyzed [5+2] cycloaddition reaction of bifunctional allenes and vinylcyclopropanes are described. The reactions proceed with facility and in yields of up to 99% with a variety of alkyne-, ester-, styrene-, or cyano-substituents on the allene to afford the corresponding cycloadducts. In the presence of CO, the reaction proceeds to an eight-membered ring cycloadduct and its transannularly closed product, providing the first example of a three-component [5+2+1] cycloaddition with allenes.

Observation of the First Heck-Type Cross-Coupling Reaction of Allenes with Aryl Halides. Synthesis of Polysubstituted 1,2-Allenyl Sulfones

[reaction: see text] The Heck-type allenylation of aryl halides with allenes has been observed for the first time: The regioselectivity of intermolecular carbopalladation of 1,2-allenyl sulfones affording vinylic Pd intermediates is completely opposite to what was reported in the literature.

JIRO TSUJI. Palladium reagents and catalysts: new perspectives for the 21st century. Wiley–VCH, 2004. 670 pp. ISBN 0470850337 (paperback)

JIRO TSUJI. Palladium reagents and catalysts: new perspectives for the 21st century. Wiley–VCH, 2004. 670 pp. ISBN 0470850337 (paperback)

An Improved Catalytic System, Pd(PPh3)4/PhCOOH Combined Catalyst, for the Allylation of Carbon Pronucleophiles with Allenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Regioselective Palladium-Catalyzed Annulation Reactions of Heteroatom-Substituted Allenes for Synthesis of Condensed Heterocycles

We have developed a highly regioselective synthesis of heterocycles via palladium-catalyzed annulation reaction of heteroatom-substituted allenes. Various aryl halides were reacted and one regioisomer was observed exclusively in all reactions. In addition, subsequent functionalizations of annulated products were carried out using alkyl metal reagents, and the introduction of alkyl moieties was accomplished.

Unusual Palladium-Catalyzed Silaboration of Allenes Using Organic Iodides as Initiators: Mechanism and Application

A highly regio- and stereoselective method for the synthesis of various 2-silylallylboronates 7 from allenes 1 and 2-(dimethylphenylsilanyl)-4,4,5,5-tetramethyl[1,3,2]dioxaborolane (5) catalyzed by palladium complexes and initiated by organic iodides is described. Treatment of monosubstituted aryl and alkylallenes RCH=C=CH(2) (1a-m) and 1,1-dimethylallene (1n) with borylsilane 5 in the presence of Pd(dba)(2) (5 mol %) and organic iodide 3a (10 mol %) afforded the corresponding silaboration products 7a-n in moderate to excellent yields. This catalytic silaboration is totally regioselective with the silyl group of 5adding to the central carbon and the boryl group to the unsubstituted terminal carbon of allene. Furthermore, the reactions show very high E stereoselectivity with the Z/E ratios lying in the range from 1/99 to 7/93. In the absence of an organic iodide, silaboration of 1 with 5 still proceeds, but gives products having completely different regiochemistry as that of 7. The silaboration chemistry can be applied to the synthesis of homoallylic alcohols. Treatment of allenes (1) with borylsilane 5 and aldehydes 14 in the presence of Pd(dba)(2) (5 mol %) and 3a (10 mol %) at 80 degrees C in ethyl acetate for 5 h afforded homoallylic alcohols 15a-p in one pot in good to excellent yields, with exceedingly high syn selectivity (>93%). Mechanistic pathways involving an unusual palladium-catalyzed three-component assembling reaction of dimethylphenylsilyl iodide, allene 1, and borylsilane 5 were proposed to account for these catalytic reactions.

Carbon−Carbon Bond Formation by Cumulene Insertion into “Rh(μ-CH2)M” Moieties (M = Ru, Os): Roles of the Cumulenes and the Metals in Product Formation

The reactions of allene, methylallene, and 1,1-dimethylallene with [RhM(CO)4(μ-CH2)(dppm)2][X] (M = Os, X = BF4 (1); M = Ru, X = CF3SO3 (3); dppm = μ-Ph2PCH2PPh2) in the presence of 1 equiv of trimethylamine oxide yield a variety of products. Under these conditions compounds 1 and 3 react with allene to yield the trimethylenemethane-bridged products [RhM(CO)2(μ-η3:η1-C(CH2)3)(dppm)2][X] (M = Os (5), Ru (6)), in which the trimethylenemethane fragment is η1-bound to the group 8 metal by one methylene group and η3-bound to Rh by the rest of the fragment. These compounds react with CO and PMe3 to yield [RhM(CO)2L(μ-η3:η1-C(CH2)3)(dppm)2][X] (L = CO, PMe3), in which L is coordinated to Rh and the η3:η1-binding mode of trimethylenemethane is retained. Although attack of L occurs at Rh for the Rh/Ru species, carbonyl attack in the Rh/Os compound initially occurs at Os with subsequent scrambling throughout the three carbonyl sites; attack of PMe3 on the Rh/Os compound occurs at Rh. Methylallene reacts with 1 and ...

Metal‐Controlled Selective [3 + 2] Cyclization Reactions of Alkenyl Fischer Carbene Complexes and Allenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereochemistry of the Asymmetric Carbopalladation of Allenes Followed by Nucleophilic Substitution Reactions with Carbo‐ and Aminonucleophiles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New and Selective Transition Metal Catalyzed Reactions of Allenes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metal-Controlled Selective [3+2] Cyclization Reactions of Alkenyl Fischer Carbene Complexes and Allenes

Chromium alkenyl Fischer carbene complexes undergo selective [3+2] cyclization reactions to allenes in the presence of nickel(0) or rhodium(I) catalysts. Interestingly, the chemo- and regioselectivity of the process are entirely dependent on the nature of the metal.

Highly Regioselective Palladium/Copper‐Catalyzed Cross‐Coupling Reactions of Terminal Alkynes and Allenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Intramolecular Hetero Diels—Alder Reactions of Vinyl Allenes and Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Octahydroquinolines Through the Lewis Acid Catalyzed Reaction of Vinyl Allenes and Imines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Additive Effects in Palladium—Indium Mediated Barbier‐type Allylations.

AbstractFor Abstract see ChemInform Abstract in Full Text.

An Improved Catalytic System, Pd(PPh3)4/PhCOOH Combined Catalyst, for the Allylation of Carbon Pronucleophiles with Allenes

The reaction of allenes with active methynes and methylenes proceeded smoothly in the presence of Pd(PPh3)4/PhCOOH combined catalyst to give the corresponding monoallylated products with E-stereoselectivity in good to high yields. This result is in marked contrast to the previous finding that the reaction of allenes with active methynes, in the presence of Pd2(dba)3·CHCl3/dppb catalyst, affords the allylation products in lower yield with lower stereoselectivities.

Stereochemistry of the asymmetric carbopalladation of allenes followed by nucleophilic substitution reactions with carbo- and aminonucleophiles.

The stereochemistry of the asymmetric palladium-catalyzed reaction of allenes with iodobenzene followed by nucleophilic substitution reaction with sodium malonate and N-methylbenzylamine is described. On the basis of the absolute configuration of the product and the stereochemical result of a similar reaction of a chiral allene, the mechanism of the above asymmetric reactions is discussed.

Lewis Acid Catalyzed Reaction of Allenes with Activated Ketone.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Transition Metal Catalyzed/Mediated Reaction of Allenes with a Nucleophilic Functionality Connected to the α‐Carbon Atom

AbstractFor Abstract see ChemInform Abstract in Full Text.