By Raimonds E. Valters, Wilhelm Flitsch (auth.), Alan R. Katritzky (eds.)

After learning ring-chain tautomerism of keto ami des and comparable derivatives of functionalized carboxylic acids for greater than ten years, the authors give some thought to it valuable to summarize on hand effects on those prototropic equilibria. First makes an attempt to systematize the cloth have been released via Jones in 1963 (Chapter 1, ref. 11). a lot, occasionally contradictory, experimental info have been scattered concerning the literature at the moment; spectroscopic equipment, utilized to this box over the last twenty years, have been had to revise a number of earlier thoughts. within the following years specific elements of ring-chain tautomerism were mentioned sometimes, yet no try was once formerly made to hide the full box. This evaluation is designed to supply a finished compilation of ring-chain tautomerism with one exception: carbohydrates that have already been taken care of many times, were passed over. The publication relies on a monograph released in Russian: R. E. Valters, Ring-Chain Isomerism in natural Chemistry. Zinatne. Riga, 1978. There­ fore, the association and improvement of the subject matter is due regularly to at least one of the authors (R.E.Y.). within the current paintings the literature has been coated until eventually the tip of 1982.

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R / . (C"o C/ C=O R / "OH (18) (1A) c=o in (IA) C /' CH 1 I CH, ,,- (JC H, "" C II H ""C, R H Me Solvent CCI 4 CCI 4 Ph dioxan CCI 3 CHCI 3 H Me Ph CCI 3 dioxan dioxan dioxan CHCI 3 (KBr) H Me dioxan Ph dioxan CCI 3 CHCI 3 Ketonic or aldehydic 1749 1726 1690 1767 1699 1706 1681 1754sh 1676 1786sh Carboxylic C=O in (18) Lactonic 1795 Refs. I7I I 1758 (free) 1714 (bonded) 1735 1724 30 19 1808 33 34 1723 1724 1726 1721 1778 1776 1781 1789 26 26 26 34 1713 1715 1795,1761 1763 1769 1812 35 22 27 34 IR method [38,39]: the ketonic band at 1670-1660 cm- 1 [39] was used as the analytical one.

Strong nucleophiles add to the c=o group, and the reaction is followed by ring opening yielding an open structure derivative (36). The amides (36, B = NHR) formed in the reactions with ammonia and primary amines may isomerize further to give hydroxylactams (3B). Weaker nucleophiles (aromatic amines, alcohols, urea, etc. [151]) replace the chlorine atom, leading to lactones (37). The direction of the reaction depends not only on the nucleophilicity of the reagent HB [lSI], but also on the structure of the chlorolactone (2B).

These phenomena were erroneously said to indicate an equilibrium (3A) ~ (3B) [199]. 80 60 ~ 40 \ 20 0 \ '0t---J - d 1 2 80 ...!! 0 . D t. D 0 20 0 V /r-... '----V ~ 6 1600 Figure 9. The splitting and the shift toward lower frequencies of the hydroxylactam C=O band in the IR spectra of ketoamide ring isomers in the solid state as compared with solution spectra: 1-2,3( CO }-benzoylen-I-ethyl-2-hydroxy-3-phenyl-5-pyrrolidone in the solid state; 2-its solution in dioxan; 3-3-hydroxy-3-phenylisoindolinone in the solid state; 4--its solution in dioxan; 5-3-hydroxy-2-isopropyl-3-phenylisoindolinone in the solid state; 6-its solution in dioxan [146, 198].

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