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    Union Catalogue of Agricultural Libraries in the Netherlands

    The WUR Library Catalogue contains bibliographic data on books and periodicals held by the libraries of Wageningen University and Research Centre and some 15 associated libraries. Holding data are added to each record.

    Subjects covered include Agrotechnology, Food and Food Production, Plant and Animal Sciences, Soil Science, Geo-information, Landscape and Spatial Planning, Water and Climate, Ecosystem Studies, Economics and Society.

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Record number 104272
Title Cine and direct aminations of 5- and 6-halogenopyrimidines : a mechanistic study
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[door] C.A.H. Rasmussen
Author(s) Rasmussen, C.A.H.
Publisher Wageningen : [s.n.]
Publication year 1978
Description 91 p.
Notes Proefschrift Wageningen
Tutors Plas, Prof. Dr. H.C. van der
Graduation date 1978-10-06
Dissertation no. 736
Author abstract show abstract
This thesis describes investigations into the mechanistic aspects of the cine amination of 4-substituted 5-halogenopyrimidines and the direct amination of 4-substituted 6-halogenopyrimidines by potassium amide in liquid ammonia.

PMR spectra of some 4-R-5-bromopyrimidines (R=C 6 H 5 , t -Bu, OCH 3 , H 3 CNC 6 H 5 , HNCH 3 , CH 3 ) in liquid ammonia containing potassium amide are reported. Evidence is presented for the formation of stable 1:1 σ-adducts by addition of an amide ion to C-6 of the pyrimidine ring in the cases of R=C 6 H 5 , t-Bu, OCH 3 and H 3 CNC 6 H 5 . When R=HNCH 3 deprotonation of the substituent occurs. In the case of R=CH 3 deprotonation is observed alongside adduct formation, the ratio of anion to σ-complex changing from 3:1 when R=CH 3 to 1:2 for R=CD 3 . This increase in σ-complex formation is ascribed to a deuterium isotope effect.

Evidence is presented that the cine substitution of 5-bromo-4- t -butyl-[1(3)- 15N] pyrimidine by potassium amide in liquid ammonia takes place to a considerable extent via an S N (ANRORC) cinemechanism. This process involves an addition of an amide ion to C-2 of the pyrimidine ring, ring opening, loss of hydrogen bromide and subsequent ring closure. A deuterium isotope effect of about 2 is observed, indicating that hydrogen (deuterium) loss is a rate-determining step in the cine amination.

No S N (ANRORC) cinemechanism, but an S N (AE) cineprocess is observed when the C-2 atom is inaccessible to the attacking amide ion, as in the cine amination of 5-bromo-2,4-di- t -butylpyrimidine.

Treatment of 4- t -butyl-5-chloro- and 5-chloro-2,4-di- t -butylpyrimidine with potassium amide in liquid ammonia yields only minor quantities of the cine sub stitution product. The 6-amino-5-chloro derivatives are obtained as main products. It is proved that no S N (ANRORC) processes are involved in this Chichibabin reaction, the amination products being formed via an S N (ANRORC) mechanism.

The nature of the substituent at C-4 in 4-R-5-bromopyrimidines influences the mechanism of the cine amination. An S N (ANRORC) cinepathway is observed when R= t -Bu, C 6 H 5 , OCH 3 or a piperidino group. If the substituent possesses an acidic proton a to the pyrimidine ring (R=CH 3 , HNCH 3 , HNC 6 H 5 and NH 2 ) deprotonation occurs and the resulting anions are converted into the corresponding 6-amino derivatives via an S N (AE) cineprocess. When R=piperidino a small amount of 2-amino-4-piperidinopyrimidine is obtained via an S N (AE) teleroute.

The occurrence of an S N (ANRORC) mechanism in the direct substitutions of 4-R-6-X-pyrimidines (X=Br or Cl) is dependent on the same characteristic structural requirements as shown for the cine amination, unhindered access of the amide ion to C-2 and absence of an acidic proton αto the heterocyclic ring on the substituent at C-4. Ring opening is observed when R= t -Bu, C 6 H 5 , OCH 3 and piperidino. An S N (AE) process is indicated when R=CH 3 (X=Br or Cl), when R=HNC 6 H 5 , (X=Cl) and in the reactions of 2,4-di- t -butyl-6-X-pyrimidines (X=Br or Cl). It is shown that the temperature can influence the percentage of the reaction that takes place via an S N (ANRORC) process considerably.

The amino-demethoxylation of 5-bromo-4,6-dimethoxypyrimidine and 4,6- dimethoxypyrimidine by potassium amide is shown to occur entirely via an S N (ANRORC) mechanism to give the corresponding 6-amino derivatives.

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On paper FORUM ; STACKS ; NN08200,736
FORUM ; STACKS ; NN08202,736
Keyword(s) (cab) halogenated hydrocarbons / organic halogen compounds / pyrimidines
Categories Organic Chemistry
Publication type PhD thesis
Language English
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