Ring, chain transform

In contrast to the 2,4-diazidopyrimidines, only one azido group is involved in ring-chain transformations of 4,6-diazidopyrimidine 342 (Scheme 134) (88DOK115).The content of the tetrazole tautomer 342AT increases... 

Ring-chain transformations and their application in the synthesis of heterocyclic compounds 99MI31. 

A ring-chain transformation with slow interconversion (compared with the NMR time-scale) has been reported in the solution of (144) and related derivatives. On the other hand, no tautomerism was observed when the benzene ring was replaced by a thiophene ring or an aliphatic double bond. ... 

Dramatic colour changes are sometimes observed in systems of compounds with the empirical formula (RE) (E = As,Sb) when ring/chain equilibria are involved and the number of element-element bonds in rings or chains is changed. The chemistry of the cycles and the related chains has been reviewed and is also dealt with in a chapter of this book. There are two principal motives for colour changes reversible formation of intermolecular contacts or ring/chain transformations. 

Ring-chain transformations and their applicationin the synthesis of heterocychc compoimds 99MI31. 

Ring transformations heterocyclic compounds reviews, 1, 70 Ring-chain tautomerism polyheteroatom six-membered rings, 3, 1056 Ripariochromene A synthesis, 3, 751, 755 Robinson-Gabriel synthesis oxazoles, 6, 216... 

There are two important rhodium-catalyzed transformations that are broadly used in domino processes as the primary step. The first route is the formation of keto carbenoids by treatment of diazo keto compounds with Rh11 salts. This is then followed by the generation of a 1,3-dipole by an intramolecular cyclization of the keto carbenoid onto an oxygen atom of a neighboring keto group and an inter- or intramolecular 1,3-dipolar cycloaddition. A noteworthy point here is that the insertion can also take place onto carbonyl groups of aldehydes, esters, and amides. Moreover, cycloadditions of Rh-carbenes and ring chain isomerizations will also be discussed in this section. 

In these studies (291, 292), the ring-chain tautomerism of silylated cations A, prepared by reversible silylation of the above mentioned nitronates (96) was suggested as an explanation for the observed transformations of y-keto-functionalized SENAs 96 (Scheme 3.80). 

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... 

N-Oxides undergo a number of side-chain transformations in which the ring system remains intact (Scheme 40). " Formation of 157 presumably occurs via the isocyanate, but attempts to trap this with water or ethanol failed. 

The Tautomerism of Heterocycles J. Elguero etal., Adv. Heterocycl. Chetn., Suppl. 1,1976. Ring-Chain Isomeric Transformations of Hydroxy-, Amino-, and Mercapto-Derivatives of Carbonyl Compounds and Their Heteroanalogues R. Valters, Russ. Chem. Rev. Engl. Transl.), 1974, 43, 665-678. 

Degradation of the sterol stigmasterol to progesterone is achieved by the sequence shown in Figure 5.120. The double bond in the side-chain allows cleavage by ozonolysis, and the resultant aldehyde is chain shortened via formation of an enamine with piperidine. This can be selectively oxidized to progesterone. In this sequence, the ring A transformations are carried out as the... 

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