- Crucial role of β-elimination in determining regio- and chemoselectivity of the rhodium-catalyzed hydroformylation of N -allylpyrroles: A new approach to 5,6-dihydroindolizines
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Rhodium-catalyzed hydroformylation of the chiral (S)-3-alkyl-3-pyrrol-1- ylprop-1-enes at 100 atmospheres total pressure and 25C led to the preferential formation of the branched 3-alkyl-2-methyl-3-pyrrol-1-ylpropanals. At 30 atmospheres and 125°C, the linear 4-alkyl-4-pyrrol-1-ylbutanals were obtained: these aldehydes are not the final products, but evolve into more stable 5,6-dihydroindolizines, with the same optical purity as the starting olefins, via a domino cyclization-dehydration process. According to the generally accepted mechanism for rhodium-catalyzed hydroformylation, the regioselectivity, and then the final chemoselectivity, can be rationalized by taking into account that while at room temperature no -elimination occurs, at high temperature the -elimination involves the branched rhodium-alkyl intermediate only.
- Settambolo, Roberta
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experimental part
p. 2915 - 2921
(2010/10/21)
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- A new class of optically active pyrrole derivatives: (3R)-3-(pyrrol-1-yl)alk-1-enes from D-α-aminoacids
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(3R)-3-(Pyrrol-1-yl)but-1-ene 4a, (3R)-4-methyl-3-(pyrrol-1-yl)pent-1-ene 4b, (3R)-3-(pyrrol-1-yl)hex-1-ene 4c in high enantiomeric excess (>92%) were prepared starting from D-α-amino acids. The crucial steps in the synthesis, reduction (DIBAH) of the corresponding pyrrolylesters to the corresponding pyrrolylaldehydes followed by Wittig olefination proceeded without compromising the stereochemical integrity.
- Settambolo, Roberta,Guazzelli, Giuditta,Mengali, Lucia,Mandoli, Alessandro,Lazzaroni, Raffaello
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p. 2491 - 2493
(2007/10/03)
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- Influence of the reaction temperature on the regioselectivity in the rhodium-catalyzed hydroformylation of vinylpyrroles
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The influence of the temperature on the regioselectivity in the hydroformylation of the vinylpyrrole isomers and of the corresponding N-tosylated substrates has been investigated in the range 20-100°C, in the presence of Rh4(CO)12. At all the temperatures the branched aldehyde was prevailing with respect to the linear isomer for all the substrates ( α-regioselectivity). With increasing temperature, an increase of the linear aldehyde was observed to a different extent in dependence on the substrate nature. 2H NMR investigation of the crude reaction mixture recovered from deuterioformylation of 3-vinylpyrrole at partial substrate conversion points out that the observed depression of the α-regioselectivity with increasing temperature must be connected to a β-hydride elimination process occurring for the branched alkyl-rhodium intermediates but not for the linear ones.
- Caiazzo, Aldo,Settambolo, Roberta,Uccello-Barretta, Gloria,Lazzaroni, Raffaello
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p. 279 - 284
(2007/10/03)
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- High α-regioselectivity in the rhodium-catalyzed hydroformylation of vinylpyrroles
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The Rh4(CO)12-catalyzed hydroformylation at low temperature (40°C) of the 1-, 2- and 3-vinylpyrrole gives the corresponding branched aldehydes 2-(1-pyrrolyl)propanal, 2-(2-pyrrolyl)propanal and 2-(3-pyrrolyl)propanal with high α-regioselectivity.
- Settambolo, Roberta,Caiazzo, Aldo,Lazzaroni, Raffaello
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p. 337 - 338
(2007/10/02)
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- Synthesis and Stereoselective Reactions of 2-(Pyrrol-1-yl)alkanals and 2-(pyrrol-1-yl)alkan-1-ones
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2-(2,5-Dimethylpyrrol-1-yl)alkanals, 2-(pyrrol-1-yl)alkanals, and 2-(2,5-dimethylpyrrol-1-yl)alkan-1-ones were prepared.The reactions of these compounds with Grignard and hydride reagents proceeded stereoselectively to give the corresponding 2-(pyrrol-1-yl)alcohols, which were converted into 2-aminoalcohols, such as norephedrine and ephedrine, by cleavage of the pyrrole ring.
- Kashima, Choji,Maruyama, Tatsuya,Fujioka, Yoko,Harada, Kazuo
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p. 1041 - 1046
(2007/10/02)
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