17282-41-6Relevant articles and documents
One-pot two-step synthesis of 1-(ethoxycarbonyl)indolizines via pyridinium ylides
Allgaeuer, Dominik S.,Mayr, Herbert
supporting information, p. 6379 - 6388 (2013/10/21)
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.
Equilibrium Acidities and Homolytic Bond Dissociation Energies of the Acidic C-H Bonds in N-Substituted Trimethylammonium and Pyridinium Cations
Zhang, Xian-Man,Bordwell, Frederick G.,Puy, Michael Van Der,Fried, Herbert E.
, p. 3060 - 3066 (2007/10/02)
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.
