Download Advances in Heterocyclic Chemistry, Vol. 74 by Henk C. van der Plas, Alan R. Katritzky PDF

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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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.

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