Intramolecular reversibility

Ring-chain tautomerism via intramolecular reversible addition reactions to the C=0 group 95AHC(64)251. 

The reversible first-order reaction (1.47) can be converted into an irreversible A X process by scavenging X rapidly and preventing its return to A. Thus the intramolecular reversible electron transfer in modified myoglobin (Sec. 5.9)... 

Recent Developments in Ring-Chain Tautomerism L Intramolecular Reversible Addition Reactions to the C = O Group ... 

This chapter is the first part of a review that updates an earlier work by R. E. Valters and W. Flitsch, Ring-Chain Tautomerism (A. R. Katritzky, ed.). Plenum Press, New York and London, 1985. The second part of this review, to be published in a subsequent volume of Advances in Heterocyclic Chemistry, includes data (1982-1993) for intramolecular reversible addition reactions to C = N, C=N, C = C, and C=C groups. 

In the second group of ring-chain tautomeric interconversions, an open-chain system is transformed into a cyclic system through the intramolecular reversible addition of a functional group to a polar multiple bond lA IB 2A 2B 3A 3B and 4A 4B. The book (I) and this article deal with... 

Ring-chain tautomeric interconversions proceeding by intramolecular reversible addition reactions to the C=0 group (Scheme 1) have been well studied, particularly with respect to the 3- and 4-oxocarboxylic acids containing five- or six-membered rings, respectively. Relatively few new investigations have appeared in the literature. 

Ring-chain equilibria involving cyclic tautomer formation by intramolecular reversible amidrazone NH-group addition to the C=0 bond were observed (85KGS849 86ZOR500) in solutions of the products formed in the reactions of pentane-2,4-dione and its 3-methyl derivatives with benzamidrazinium iodides. The ring-chain equilibrium was detected only in solutions of iodides or picrates. The free bases exist as the open-chain tautomers, like the hydrazones or enhydrazines. In contrast with the acyl-... 

On the other hand, an intramolecular reversible rotation of the two mesityl rings in 2,2-dimesityl-l-(trimethylsilyl)ethenol (202) occurs to give 203 (equation 83)258. The free energy of activation for the rotation (AG ) leading to the enantiomerization is... 

Valters, R. E., Ffilop, F., Korbonits, D., Recent Developments in Ring-Chain Tautomerism I. Intramolecular Reversible Addition Reaction of the C = 0 Group,... 

III. Intramolecular Reversible Addition Reactions to Other Groups. 54... 

Despite the lower reactivity of the azomethine group as compared with the carbonyl group, intramolecular reversible nucleophilic additions of OH, NH, or SH groups to the C=N bond often proceed. The intramolecular addition of nucleophilic groups to the C=N bond can occur along two pathways (endo and exo), depending on the orientation of the azomethine group in the molecule. 

Ring-chain tautomerism established by intramolecular reversible N — H group addition to the hydrazone C=N bond has been studied in a wide series of derivatives with different structures containing hydrazone N — H groups [for a review, see (88KGS3)]. The cyclic tautomers mostly involve five- or six-membered rings. 

Tsai, T.-G., Yu, C.-H. Effect of orbital overlap in thermal reverse homo-Diels-Zklder reactions and an intramolecular reverse ene reaction. J. Chin. Chem. Soc. (Taipei) 1994,41,631-634. 

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