Imide, Imidoide und Enamide

Intramolecular Reversible Addition Reactions to the C=O Group

“…Flitsch isolated [33,231] both isomers (45A, R I = Me, R2 = H) and (45B) of levulinic amide. The isomerization (45B) -+ (45A) was accomplished at 100°.…”

“…Both opposing effects may explain the increased stability of the ring isomer for N-methylamides only. A great number oflevulinic [33,189,199,218,220,230,231,234,235], other 3-acylpropionic (R 1 = alkyl) [199,220,236,237], 3-aroylpropionic [33,197,199,202,203], and methylsubstituted acylpropionic [141,200,221,231,237,238] ami des were synthesized and their structures strictl,Y proven by means of spectroscopic methods. But one rarely succeeded in obtaining both individual isomers.…”

“…3-Acylpropionic amides, bearing methyl groups in the chain, predominantly, also possess a cyclic structure [141,200,221,231,237,238].…”

“…Sheiman, Denisova, and Berezovskii [231,248,249] using the IH-NMR method have observed the tautomeric equilibria (47A) ~ (47B) which are displaced toward the cyclic tautomer in the case of N -unsubstituted and N-arylamides of 3,3,dimethyllevulinic acid. The situation is complicated by a dehydration of (47B) to give methylenepyrrolidone (48) which takes place under the condition of ring-chain equilibration in non-aqueous solutions.…”

“…Table 10 shows that electron-withdrawing substituents X in the benzene ring destabilize the cyclic form and shift the equilibrium toward (47 A) (see also [231]). The thermodynamic data tJ.H and tJ.S were calculated from the KT temperature dependence.…”