Rearrangements in heterocyclic systems

R. E. Ireland and J. P. Vevert, A chiral total synthesis of (—) and (+) nonactic acids from carbohydrate precursors and the definition of the transition for the enolate Claisen rearrangement in heterocyclic systems, J. Org. Chem. 45 4259 (1980). 

The Claisen rearrangement has also been observed in heterocyclic systems, for example see ref. 144. 

Rearrangements of TV-chloro compounds in heterocyclic systems have been studied. TV-Chloroindole 51 gives62 the 3-chloro isomer 52. With pyrrole (53) there are two... 

Moody, C. J., Azodicarbonyl Compounds in Heterocyclic Synthesis, 30, 1 Claisen Rearrangements in Heteroaromatic Systems, 42, 203. 

Claisen rearrangements in heteroaromatic systems, 42, 203 in nitrogen heterocyclic systems, 8, 143 Complex metal hydrides, reduction of nitrogen heterocycles with, 6, 45 39, 1 Concept of aromaticity in heterocyclic chemistry, 56, 303 Condensed heterocyclo[n,m- , b, or cjquinazolines, 52, 1 Condensed 4-thiazolidinones, 49, 1... 

Moody, C. J. Claisen rearrangements in heteroaromatic systems. Adv. Heterocycl. Chem. 1987,42, 203-244. 

Greci, L., Carloni, P., Stipa, P. Acid catalyzed rearrangements on indole systems. Wagner-Meerwein type transpositions. Topics in Heterocyclic Systems Synthesis, Reactions and Properties 1996, 1, 53-61. 

The analysis of published data has shown that the main drawback of the methods listed was their limited use in the synthesis of benzimidazole derivatives. For instance, for synthetic chemists it is a challenge to introduce a heterocycle into the position 2 of benzimidazole. In addition to the methods mentioned, examples of the formation of benzimidazole derivatives by rearrangement of heterocyclic systems are documented. Despite the fact that the publications on these reactions are much fewer as compared with the PhiUips-Ladenburg and Weidenhagen reactions, they are more diverse but unfortunately not general. The generalization and systematization of data published on the rearrangement reactions will considerably facilitate... 

Mamedov VA, Zhukova NA, Beschastnova TN, Gubaidullin AT (2011c) Benzimidazoles and related heterocycles 11. A novel acid-catalyzed rearrangement in the system 3-benzoylquinoxalin-2(lfl)-one-aldehyde-ammonium acetate as a simple and efficient route to 2-(imidazol-4-yl)benzimidazoles. Russ Chem Bull, Int Ed 60(5) 933-936. doi 10.1007/... 

In this section three main aspects will be considered. Firstly, the basic strengths of the principal heterocyclic systems under review and the effects of structural modification on this parameter will be discussed. For reference some pK values are collected in Table 3. Secondly, the position of protonation in these carbon-protonating systems will be considered. Thirdly, the reactivity aspects of protonation are mentioned. Protonation yields in most cases highly reactive electrophilic species. Under conditions in which both protonated and non-protonated base co-exist, polymerization frequently occurs. Further ipso protonation of substituted derivatives may induce rearrangement, and also the protonated heterocycles are found to be subject to ring-opening attack by nucleophilic reagents. 

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