- One-pot two-step synthesis of 1-(ethoxycarbonyl)indolizines via pyridinium ylides
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Pyridinium salts Py+-CH2-EWG (EWG = CO2Et, CONEt2, CN, COMe, COPh) reacted with Michael acceptors Ar-CH=C(CO2Et)(Acc) (Acc = CO2Et, COMe, SO2Me, CONH2) at ambient temperature in the presence of base to give [3 + 2]-cycloadducts by stepwise [3 + 2]-cycloaddition of the intermediate pyridinium ylides. Treatment of the crude reaction mixtures with 1 equiv. of chloranil and atmospheric oxygen in the presence of sodium hydroxide gave 1-(ethoxycarbonyl)indolizines by dehydrogenation and elimination of the acceptor group (Acc). A good yield of indolizine was also obtained from Py +-CH2CN and iPr-CH=C(CO2Et)2, which indicates that this method is not restricted to aromatic Michael acceptors. Structurally related isoquinolinium salts react with Michael acceptors analogously to give pyrrolo[2,1-a]isoquinolines.
- Allgaeuer, Dominik S.,Mayr, Herbert
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supporting information
p. 6379 - 6388
(2013/10/21)
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- Indolizines 4. The synthesis of new 3-vinylindolizines.
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New 3-vinylindolizines have been synthesized by two methods.The first strategy calls for the Wittig olefination of 3-acylindolizines with methylenetriphenylphosphorane or methoxymethylenetriphenylphosphorane.The best yields are obtained when the ylid is formed at room temperature and the condensation in refluxing THF.The required 3-acylindolizines were obtained by direct acylation of indolizines or by 1,3-dipolar cyclo-additions to acylmethylpyridinium ylids.The following 3-isopropenylindolizines were made with good yields: unsubstituted (18, 85percent), 2-methyl (10, 98percent), 2-C6H5 (17, 95percent), 1-COOMe (20, 98percent), 1-COOMe-2-C6H5 (22, 91 percent), 1,2-di-COOMe (24, 58percent).Also synthesized are the following 3-α-styrylindolizines: 2-C6H5 (19, 99percent), 1-COOMe (21, 93percent), 1-COOMe-2-C6H5 (23, 87percent), 1,2-diCOOMe (25, 66percent). 3-(α-Methyl-β-methoxyvinyl)indolizines E (26, 40percent) and Z (27, 40percent) were also obtained.The second strategy involves the 1,3-dipolar cyclo-addition of dipolarophiles to allylpyridinium ylids.The following new 3-vinylindolizines have been synthesized: 1-carbomethoxy-3-vinylindolizine (30, 21percent), 1,2-dicarbomethoxy-3-vinylindolizine (31, 16percent), 1-carbomethoxy-3-β-styrylindolizine (33, 43percent), 3-β-styrylindolizine (34, 17percent), 1-carbomethoxy-3-(β-carbomethoxy)vinylindolizine 38 (31percent).
- Bue, G. De,Nasielski, J.
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- Equilibrium Acidities and Homolytic Bond Dissociation Energies of the Acidic C-H Bonds in N-Substituted Trimethylammonium and Pyridinium Cations
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Equilibrium acidities (pKHAs) of the cations in sixteen N-substituted trimethylammonium salts, one N-phenacylquinuclidinium salt, eight N-substituted pyridinium salts, and N-(ethoxycarbonyl)-isoquinolinium bromide, together with the oxidation potentials of their conjugate bases, have been determined in dimethyl sulfoxide (DMSO) solution.The acidifying effects of the α-trimethylammonium groups (α-Me3N+) and the α-pyridinium groups (α-PyN+) on the adjacent acidic C-H bonds in these cations were found to average about 10 and 18 pKHA units, respectively, in DMSO.The homolytic bond dissociation energies of the acidic C-H bonds in these cations, estimated by the combination of the equilibrium acidities with the oxidation potentials of their corresponding conjugate bases (ylides), show that the α-trimethylammonium groups destabilize adjacent radicals by 2-6 kcal/mol, whereas α-pyridinium groups stabilize adjacent radicals by 3-6 kcal/mol.The effects of α-pyridinium groups on the stabilization energies of the radicals derived from these cations were found to be ca. 4-10 kcal/mol smaller than those of the corresponding phenyl groups, whereas their effects on the equilibrium acidities of the cations were 5.4-13.1 pKHA units larger.The pKHA value of tetramethylammonium cation (Me4N+) was estimated by extrapolation to be about 42 in DMSO.
- Zhang, Xian-Man,Bordwell, Frederick G.,Puy, Michael Van Der,Fried, Herbert E.
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p. 3060 - 3066
(2007/10/02)
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