By Henk C. van der Plas, Alan R. Katritzky
Degenerate ring adjustments of heterocycles are labeled as reactions within which a heterocyclic method is switched over into an analogous hetercyclic approach. This monograph covers an authoritative, complete review of a number of degenerate ring modifications in 5- and 6-membered heterocycles. It exhibits how by way of 15N-labeled, 13C-labeled or selectively substituted compounds those degenerate ring trnasformations will be stumbled on and hwo lots of the effects will be defined through the Addition Nucleophile, Ring starting, Ring Closure [ANRORC] mechanism. one other major topci of the monograph is the occurance of degenerate ring variations.
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Extra info for Advances in Heterocyclic Chemistry, Vol. 74
The 6-amino1,6-dihydropyrimidinides 50. These results, combined with those obtained in the amination of 2-halogeno- as well as 4-halogenopyrimidines, showing a ring-opening, ring-closure reaction sequence, raised serious doubts about 42 SN(ANRORC) SUBSTITUTIONS IN DIAZINES the correct interpretation of the chemistry of the amino-debromination of the 5-bromopyrimidines and induced a reinvestigation. , 56 (77RTC101). The retrieved starting material 51 has not undergone any decrease in 15N content.
Amination of 5-phenylpyrimidine with 15N-labeled potassium amide revealed that no label was incorporated in the pyrimidine ring of 6-amino-5phenylpyrimidine; this means that exclusively 72 has been formed. However, in 2-amino-5-phenylpyrimidine, the pyrimidine ring did contain the 15N label. From the mass spectral data it was calculated that the ratio 70 : 73 is about 20 : 80, proving that about 80% of 5-phenylpyrimidine participates in the SN(ANRORC) mechanism. 34). 4-t-Butylpyrimidine. Reaction of 4-t-butylpyrimidine with potassium amide/liquid ammonia provided a mixture of both 2-amino-4-t-butyl(25%) and 6-amino-4-t-butylpyrimidine (40%) (82RTC367).
Apparently a carbon–nitrogen skeleton rearrangement has taken place. Although an extensive discussion of this ring transformation is beyond the scope of this book, it is evident that in this pyrimidine-to-1,3,5triazine conversion the initial addition of the amide ion has to take place at another position than that on which the chloro atom is present. Proof for addition at C-6 is provided by tracer experiments (67RTC15) and 1H and 13 C NMR spectroscopy (73RTC1232; 75OMR86). 21). 21 Quite surprisingly, no ring transformation but aminodechlorination was found when 5-R-4-chloro-2-phenylpyrimidines (37, R ϭ OCH3, OC2H5, SCH3, C6H5) were subjected to treatment with potassium amide/liquid ammonia.