- ALKYLATION ORIENTATION RULES IN CONJUGATE ADDITION OF GRIGNARD REAGENTS TO NITROPYRROLE AND NITROTHIOPHENE SYSTEMS
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Conjugate addition of various Grignard reagents to 1-alkyl-2-nitropyrroles and to 2-nitrothiophene has been investigated. 1-Alkyl-2-nitropyrroles undergo alkylation at 3 and 5 positions with prevalence of the latter isomer.On the contrary, in the 2-nitrothiophene system, formation of the 3-isomer prevails.In both systems, a bulkier Grignard reagent favours the 5-isomer formation.This trend can be reversed increasing steric hindrance exerted by the 1-substituent of 2-nitropyrrole. 1-(Tri-isopropylsilyl)-3-nitropyrrole and 3-nitrothiophene give exclusively the 2-isomer.This reaction allows 2-alkyl-3-nitrothiophenes and pyrroles to be synthesized with a one-pot procedure instead of the classical multi stage reaction.
- Ballini, Roberto,Bartoli, Giuseppe,Bosco, Marcella,Dalpozzo, Renato,Marcantoni, Enrico
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p. 6435 - 6440
(2007/10/02)
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- 1-AZABICYCLIC COMPOUNDS. 24. SELECTIVITY OF POSITION OF NITRATION OF 1,2-DIHYDROPYRROLIZINE, 5,6,7,8-TETRAHYDROPYRROCOLINE AND PYRROLE HOMOLOGS
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The selectivity of the position of nitration of 1-methylpyrrole, 1,2-dimethylpyrrole, 1,2-dihydropyrrolizine, and 5,6,7,8-tetrahydropyrrocoline was found.In contrast to the selectivity of substitution during nitration of their carbocyclic analogs, o-xylene, indane, and tetraline, the fraction of the α-nitro-isomer in the nitration products of 1,2-dimethylpyrrole is smaller than the fraction of α-nitro derivatives of 1,2-dihydropyrrolizine and 5,6,7,8-tetrahydropyrrocoline, and in the latter cases the isomers are almost equally distributed.During nitration of the above bicyclic pyrroles, the Mills-Nixon effect does not appreciably influence the selectivity of the position of the reaction.
- Skvortsov, I. M.,Astakhova, L. N.
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p. 1189 - 1191
(2007/10/02)
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- PREPARATIVE ASPECTS OF THE NITRATION OF 1-METHYLPYRROLE DERIVATIVES. 13C NMR OF SOME NITROPYRROLES.
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The nitration of 1-methylpyrrole and 1,2-dimethylpyrrole was studied and the products were characterized. It was found that the nitration of ethyl 1-methylpyrrole-2-carboxylate depends on the reaction conditions. **1**3C parameters have been determined for several 1-methyl substituted pyrrole- and nitropyrrole derivatives and the relationship between the observed and predicted **1**3C shifts for aromatic carbons is briefly discussed. It has been found that the determination of the direct **1**3C-**1H coupling constants in the pyrrole ring constitutes a useful tool for distinguishing alpha - and beta -positions.
- Grehn
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