Abstract:Die Synthesen optisch aktiver N‐Acyl‐1,2,3,6‐tetrahydropyridine und deren Pd/C katalysierten Umlagerungen zu N‐Acylenaminen werden beschrieben.
“…However, omission of the phosphine and the amine (both capable of reducing palladium(II) from the reaction mixture) afforded a completely inactive isomerization catalyst. It has been demonstrated that Pd/C catalyzes the transformation of N -acyl-1,2,5,6-tetrahydropyridines to enamides . Pd/C in the absence of phosphine/amine exhibits isomerization capacity also in our catalytic system. 1 …”
Section: Discussionmentioning
confidence: 68%
“…The arylated cyclic enamides isolated can in principle undergo further regiocontrolled functionalizations both in the α-positions and β-positions to the nitrogen atom. 40b, Subsequent hydrogenation of the arylated enamides offers an alternative route to 3-arylpyrrolidines, and this competes favorably with other existing methods …”
Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds. The olefin undergoes two types of palladium-catalyzed reactions: (a) arylation to provide C-3 arylated derivatives and (b) competing double bond isomerization. Addition of silver carbonate and thallium acetate fully suppressed the isomerization, and good yields of C-3 substituted compounds were achieved after arylation with aryl halides. With regard to aryl triflates as arylating agents, addition of lithium chloride was necessary to promote the Heck reaction. This additive excluded the use of silver and thallium salts, but high regioselectivity and good yields could be obtained by employing tri-2-furylphosphine as ligand. Arylation was rendered both regioselective and enantioselective (58% ee) with 1-naphthyl triflate as substrate utilizing a (R)-BINAP/thallium acetate combination. The C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.
“…However, omission of the phosphine and the amine (both capable of reducing palladium(II) from the reaction mixture) afforded a completely inactive isomerization catalyst. It has been demonstrated that Pd/C catalyzes the transformation of N -acyl-1,2,5,6-tetrahydropyridines to enamides . Pd/C in the absence of phosphine/amine exhibits isomerization capacity also in our catalytic system. 1 …”
Section: Discussionmentioning
confidence: 68%
“…The arylated cyclic enamides isolated can in principle undergo further regiocontrolled functionalizations both in the α-positions and β-positions to the nitrogen atom. 40b, Subsequent hydrogenation of the arylated enamides offers an alternative route to 3-arylpyrrolidines, and this competes favorably with other existing methods …”
Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds. The olefin undergoes two types of palladium-catalyzed reactions: (a) arylation to provide C-3 arylated derivatives and (b) competing double bond isomerization. Addition of silver carbonate and thallium acetate fully suppressed the isomerization, and good yields of C-3 substituted compounds were achieved after arylation with aryl halides. With regard to aryl triflates as arylating agents, addition of lithium chloride was necessary to promote the Heck reaction. This additive excluded the use of silver and thallium salts, but high regioselectivity and good yields could be obtained by employing tri-2-furylphosphine as ligand. Arylation was rendered both regioselective and enantioselective (58% ee) with 1-naphthyl triflate as substrate utilizing a (R)-BINAP/thallium acetate combination. The C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.
“…Thus, we examined N ‐debenzylation of 2a under the typical hydrogenolysis conditions, as shown in Scheme . Interestingly, a double bond isomerization to 1,4,5,6‐tetrahydropyridine derivative 3 was observed unexpectedly …”
“…[134]- [136] It is therefore not surprising that double bond isomerization sometimes competes with arylation, in particular, in cases in which alkenes with allylic substituents are subjected to traditional Heck reaction conditions. [137] The arylation of the cyclic allylamine derivative in Scheme 32, which is prone to undergo isomerization, constitutes an illustrative example in which a mixture of compounds is formed.…”
Section: Bix Double Bond Migration Prior To Arylationmentioning
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