Recent advances in the neodymium catalysed polymerisation of 1,3-dienes

The benefits of using a homogeneous neodymium-based catalyst for the industrial “high cis” polymerisation of 1,3-butadiene are underlined. Preformed homogeneous catalysts for the “high cis” polymerisation of 1,3-butadiene based on Nd(carboxylate)₃/diisobutylaluminium hydride/^tbutyl chloride have been examined. The effects of changing (a) the order of catalyst component addition, (b) the carboxylate component and (c) the halogen component, on catalyst homogeneity, activity and polymer characteristics have been examined.     

Polymerization of butadiene by neodymium catalysts on oxide supports

The suspension polymerization of butadiene in hexane and toluene in the presence of catalysts composed of organoaluminum compounds and neodymium versatate applied on oxides (Al₂O₃, aluminum silicate A-14, Aerosil A-300, and white soot BS-200) has been studied. Triisobutylaluminum and its combination with ethylaluminum sesquichloride are used as organoaluminum compounds. The activity and stereospecificity of the catalysts has been found to depend strongly on the nature of supports. Catalysts based on Aerosil and white soot appear to be the most active. With the use of these catalysts, polybutadiene containing up to 97.5% 1,4-cis-units has been synthesized.     

Synthesis of 1-nitro-1,3-dienes via nitrotrifluoroacetoxylation of 1,3-dienes

Nitrotrifluoroacetate adducts, obtained from 1,3-dienes by reaction with ammonium nitrate in trifluoroacetic anhydride, readily eliminate to afford 1-nitro-1,3-dienes in high yield.     

Cycloaddition reactions of 1,3-diazabuta-1,3-dienes with alkynyl ketenes

The cycloaddition reactions of ‘all-carbon’ 1,3-diazabuta-1,3-dienes with a few conjugated and unconjugated alkynyl ketenes are described. The reactions provide some interesting azetidinones and dihydropyrimidinones bearing an alkynyl moiety. The regiochemistry of cycloadduct is related with the degree of conjugation of the alkynyl ketene. Moreover, two alternative approaches to ‘all-carbon’ 1,3-diazabuta-1,3-dienes are reported.     

Cross-metathesis of 1,3-dienes with electron-deficient olefins

Cross-metathesis reactions between 1,3-dienes and electron-deficient olefins have been investigated. Terminal monosubstituted 1,3-dienes afforded low yields of the desired CM products due to competing cleavage of the internal double bond. This undesired cleavage is successfully suppressed in the case of 1,3-dienes containing a sterically more congested internal double bond. Methyl vinyl ketone as the coupling partner was shown to provide the best yields.     

Diels-Alder reaction of methyl coumalate with 1,3-dienes

Reaction of methyl coumalate (1b) with 1,3-butadienes at 100° afforded the tetrahydrocoumarins (6) and the 4-methoxycarbonyltricyclo[3.2.1.0^2,7]octenes (7). The similar reaction of 1b with cyclohexadiene gave exclusively tetrahydronaphthalene-2-carboxylate. With cyclopentadiene, 1b afforded a product (10) resulting from the addition reaction in which cyclopentadiene acted as a dienophile. The reaction giving 6 is the first example of the reaction of a 2-pyrone as a dienophile.     

The reaction of phosphinyl radicals with 1,3-dienes

The stabilized radical, [(Me₃Si)₂CH]₂P·, reacts with 1,3-dienes to afford 1,4-diphosphino-2-butenes.     

Selenosulfonation of 1,3-dienes: One-pot synthesis of 2-(phenylsulfonyl)-1,3-dienes

A one-pot procedure for the transformation of a 1,3-diene into the corresponding 2-(phenylsulfonyl)-1,3-diene was developed. The reaction involves a 1,2-selenosulfonation-oxidation sequence.     

Silyl-titanation of acetylenes and 1,3-dienes

A Ti^IIISi active species, Cp₂TiSiMe₂Ph, is formed either by the reaction of Cp₂TiCl₂ with two equivalents of PhMe₂SiLi or by the reaction of Cp₂TiCl with one equivalent of PhMe₂SiLi. Highly regio- and stereo-selective silyltitanation by this species has been observed with acetylenes and 1,3-dienes.     

Hydrosilylation of 1,3-dienes by phenylsilane

Conclusions It was established that the catalytic system Ni(acac)₂+AlEt₃ has a high reactivity in the hydrosilylation of conjugated dienes by phenylsilane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1888–1889, August, 1975.     

Reaction of trifluororacemic acid methyl ester with 1,3-dienes

The reaction of trifluororacemic acid with 1,3-dienes affords Diels-Alder reaction products in a high yield and with a high degree of specificity. Catalysis by SnCl₄ changes the course of the reaction of the ester with isoprene, affording an ene reaction product.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 141–145. January, 1991.     

Palladium-catalyzed 1,4-acetoxy-trifluoroacetoxylation of 1,3-dienes

Palladium-catalyzed oxidation of conjugated dienes in acetic acid containing CF₃COOH/LiOOCCF₃ results in the formation of 1-acetoxy-4-trifluoroacetoxy-2-alkenes.     

Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes

Advances in the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes are presented according to substrate types and chiral monophosphine ligands. Chiral monodentate phosphine ligands with a binaphthyl moiety have been proven to be the most efficient ligands for cyclic 1,3-dienes, and planar chiral ferrocenylmonophosphine ligands with two ferrocenyl moieties for linear 1,3-dienes. The ferrocenylmonophosphine ligands have expanded the substrate scope to 1,3-enynes in the asymmetric hydrosilylation. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes and 1,3-enynes leads to the stereoselective synthesis of allylsilanes and allenylsilanes, respectively.     

Cycloaddition reaction of methyl 2-pyronecarboxylates with 1,3-dienes

The experimental results of thermal cycloaddition reactions of methyl 2-pyrone-3-, 4-, 5- and 6-carboxylates with 1,3-dienes and the theoretical approach by a second order perturbation MO method are described. The sequential introduction of a methoxycarbonyl group onto a 2-pyrone ring caused a variety of selectivities in the cycloaddition reactions with 1,3-butadienes. PMO treatment based only on the frontier molecular orbitals failed to account adequately for this selectivity phenomena because the relative magnitudes of the coefficients in the HO and LU orbitals of 2-pyrones were little affected by the introduction of a substituent. PMO treatment including superjacent and subjacent orbitais along with frontier orbitais rationalized excellently the observed selectivity phenomena.     

Cycloaddition reactions of 2,4-diphenyl-1,3-diazabuta-1,3-dienes with isocyanates and isothiocyanates

The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed.