- FACILE SYNTHESIS OF ACETYLENECARBOXYLATES BY THE OXIDATIVE CARBONYLATION OF TERMINAL ACETYLENES CATALYSED BY PdCl2 UNDER MILD CONDITIONS
-
Terminal acetylenes were converted to acetylenecarboxylates in high yields under athmospheric pressure of carbon monoxide at room temperature using a catalytic amount of PdCl2 and a stoichiometric amount of CuCl2.
- Tsuji, Jiro,Takahashi, Mitsuo,Takahashi, Takashi
-
-
Read Online
- Palladium-catalyzed carbonylation of terminal acetylenes: A new method for synthesis of acetylenecarboxylates
-
Acetylenecarboxylates were easily prepared via palladium bromide-catalyzed carbonylation of terminal acetylenes in fair to good yields.
- Li,Jiang,Chen
-
-
Read Online
- Novel insights into cyclooxygenases, linoleate diol synthases, and lipoxygenases from deuterium kinetic isotope effects and oxidation of substrate analogs
-
Cyclooxygenases (COX) and 8R-dioxygenase (8R-DOX) activities of linoleate diol synthases (LDS) are homologous heme-dependent enzymes that oxygenate fatty acids by a tyrosyl radical-mediated hydrogen abstraction and antarafacial insertion of O2. Soybean lipoxygenase-1 (sLOX-1) contains non-heme iron and oxidizes 18:2n - 6 with a large deuterium kinetic isotope effect (D-KIE). The aim of the present work was to obtain further mechanistic insight into the action of these enzymes by using a series of n - 6 and n - 9 fatty acids and by analysis of D-KIE. COX-1 oxidized C20 and C18 fatty acids in the following order of rates: 20:2n - 6 > 20:1n - 6 > 20:3n - 9 > 20:1n - 9 and 18:3n - 3 ≥ 18:2n - 6 > 18:1n - 6. 18:2n - 6 and its geometrical isomer (9E,12Z)18:2 were both mainly oxygenated at C-9 by COX-1, but the 9Z,12E isomer was mostly oxygenated at C-13. A cis-configured double bond in the n - 6 position therefore seems important for substrate positioning. 8R-DOX oxidized (9Z,12E)18:2 at C-8 in analogy with 18:2n - 6, but the 9E,12Z isomer was mainly subject to hydrogen abstraction at C-11 and oxygen insertion at C-9 by 8R-DOX of 5,8-LDS. sLOX-1 and 13R-MnLOX oxidized [11S- 2H]18:2n - 6 with similar D-KIE (~ 53), which implies that the catalytic metals did not alter the D-KIE. Oxygenation of 18:2n - 6 by COX-1 and COX-2 took place with a D-KIE of 3-5 as probed by incubations of [11,11- 2H2]- and [11S-2H]18:2n - 6. In contrast, the more energetically demanding hydrogen abstractions of the allylic carbons of 20:1n - 6 by COX-1 and 18:1n - 9 by 8R-DOX were both accompanied by large D-KIE (> 20).
- Hoffmann, Inga,Hamberg, Mats,Lindh, Roland,Oliw, Ernst H.
-
-
Read Online
- Synthesis of the ω6 (5z,8z)-tetradecadienoic and (7z,10z)-hexadecadienoic polyene fatty acids
-
An approach using acetylenes was used and optimized to synthesize rare natural ω6 polyene fatty acids. The key synthetic step was cross-coupling of a propargyl derivative with a terminal acetylene in the presence of equimolar amounts of Cu(I).
- Golovanov,Ganina,Groza,Eremin,Myagkova
-
-
Read Online
- Palladium-mediated cross-coupling reactions involving 3-substituted alkyl (E)-2,3-dibromopropenoates and arylzinc or aryltin derivatives
-
Stereodefined unsymmetrically 3,3-disubstituted alkyl 2-bromopropenoates, 5, were regioselectively prepared by Pd-mediated reactions between 3-alkyl, 3-aryl and 3-alkoxycarbonyl substituted (E)-2,3-dibromopropenoates, (E)-7, and aryl or 1-alkynylzinc chlorides. The stereospecificity of these reactions was found to be dependent on the type of substituent present in the 3-position of (E)-7. The (E)-stereochemistry of compounds 5b, 5d and 5i so prepared was confirmed by their conversion into the corresponding 4-substituted 3-bromocoumarins. Tetrasubstituted α,β-unsaturated esters 10 were then synthesized by Pd-mediated reactions either of (E)-7 with a molar excess of an arylzinc chloride or an aryltributylstannane, or of a compound of general formula 5 with an aryltributylstannane. An examination of the parameters which influence the stereochemistry and the yields of these arylations was made.
- Rossi, Renzo,Bellina, Fabio,Carpita, Adriano,Mazzarella, Felice
-
-
Read Online
- Palladium-catalyzed oxidative carbonylation of 1-alkynes into 2-alkynoates with molecular oxygen as oxidant
-
A new preparative method to produce alkyl 2-alkynoates from 1-alkynes in alcohol under atmospheric pressure of CO at room temperature was developed with palladium-phosphine catalysts, using molecular oxygen as an oxidant. On the basis of the behavior of model complexes such as methoxycarbonylpalladium and alkynylpalladium complexes, we propose a mechanism accounting for the catalytic carbonylation of alkynes through an intermediate having the both methoxycarbonyl and alkynyl ligands that liberates methyl 2-alkynoates and a Pd(0) species on reductive elimination. The oxidation of Pd(0) to Pd(II) species in the presence of a halide ion was confirmed to proceed cleanly with molecular oxygen as the oxidant. On the basis of the findings on homogeneous catalysts, a heterogeneous catalytic system using Pd/C has also been developed.
- Izawa, Yusuke,Shimizu, Isao,Yamamoto, Akio
-
p. 2033 - 2045
(2007/10/03)
-
- Synthesis of 2-acetylenic carboxylic acids, 1-sulfinyl and 1-sulfonyl- 2-ketones from 2-acetylenic phenyl sulfides
-
Monochlorination at the 1-position with sulfuryl chloride, followed by methanolysis converted 2-acetylenic phenyl sulfides into 1-methoxy-2- acetylenic phenyl sulfides. Oxidation with chromic acid gave 2-acetylenic carboxylic acids. Oxidation of 2-acetylenic phenyl sulfides with Oxone and hydrogen peroxide in acetic acid gave the corresponding sulfoxides and sulfones respectively. Diethylamine addition to the triple bond produced enamines which were hydrolyzed with aqueous hydrochloric acid to the corresponding 1-sulfinyl and 1-sulfonyl-2-ketones.
- Fortes, Carlos C.,Garrote, Clevia F.D.
-
p. 2993 - 3026
(2007/10/03)
-
- Stereoselective Synthesis of 1,4-Dienes. Application to the Preparation of Insect Pheromones (3Z,6Z)-Dodeca-3,6-dien-1-ol and (4E,7Z)-Trideca-4,7-dienyl Acetate
-
Stereoselective synthesis of Z,E- and Z,Z-1,4-dienes has been achieved by the cross-coupling of allylic substrates with vinyl organometallic reagents.Key to this strategy was the development of a method for regiospecific incorporation of a tri-n-butylstannyl group in the γ-position of the allylic cross-coupling partner.The steric bulk of this moiety ensures the stereochemical integrity of the allylic double bond throughout the coupling sequence and is easily replaced by hydrogen in the coupled product.This strategy has been applied to the synthesis of the termite trail marker pheromone 22 and the leafminer moth sex pheromone 28.
- Hutzinger, Michael W.,Oehlschlager, Allan C.
-
p. 4595 - 4601
(2007/10/02)
-