1,3-Butadiene, 1-methoxy-, hydrogenation

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

More recently, using the cyclometallated iridium C,(7-benzoate derived from allyl acetate, 4-methoxy-3-nitrobenzoic acid and BIPHEP, catalytic carbonyl crotylation employing 1,3-butadiene from the aldehyde, or alcohol oxidation was achieved under transfer hydrogenation conditions [274]. Carbonyl addition occurs with roughly equal facility from the alcohol or aldehyde oxidation level. However, products are obtained as diastereomeric mixtures. Stereoselective variants of these processes are under development. It should be noted that under the conditions of ruthenium-catalyzed transfer hydrogenation, conjugated dienes, including butadiene, couple to alcohols or aldehydes to provide either products of carbonyl crotylation or p,y-enones (Scheme 16) [275, 276]. 

Scheme 3.16 Products of the hydrogenation of trans- 1-methoxy- 1,3-butadiene.

Further extension of the reaction pool of Schilf bases 138 was achieved by their reaction with tran -l-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky s diene) to give 2-substituted 5,6-didehydro-piperidin-4-ones 164 [135,136] (Scheme 10.54). The reaction is considered to be a sequence of an initial Mannich reaction between the imine and the silyl enol ether, followed by an intramolecular Michael addition and subsequent elimination of methanol. If the reaction was terminated by dilute ammonium chloride solution, then the Mannich bases 163 could be isolated and further transformed to the dehydropiperidinones 164 by treatment with dilute hydrochloric acid. This result proved that the reaction pathway is not a concerted hetero Diels-Alder type process between the electron-rich diene and the activated imine. The use of hydrogen chloride as a terminating agent resulted in exclusive isolation of the piperidine derivatives 164 formed with... 

Ethylhexanol Glycidyl ether 100 Heptane Hexafluoropropylene/vinylidene fluoride copolymer HexafIuoropropylene/vinyIidene fluoride/tetrafluoroethylene terpolymer 2-Hexyl decanoic acid Hydrogenated butadiene/acrylonitrile copolymer Hydrogenated rapeseed oil fatty acid Hydroxylamine sulfate Lauryl alcohol Methacrylonitrile 2-Methoxy-5-nitroaniline n-Nonane 2-Octyl dodecanoic acid Oleamine Oxalic acid PEG-8 dimethacrylate Phenyl dimethicone Piperazine dihydrochloride Polynorbomene... 

Dimethoxy-l,4-benzoquinone adds to 3-chloro-l-methoxy-l,3-butadiene in various solvents (Eq. 11). The primary adduct eliminates methanol and aromatizes spontaneously. The reaction is practically quantitative in toluene after 3.5 h of irradiation. An important effect is also observed in methylene chloride solution, where the rate increase reaches a factor of >10. If in this solvent a catalysis by in situ generated hydrogen chloride is possible, another explanation must be found for the sonochemical effect observed in benzene or toluene solution. 

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