By Henk C. van der Plas, Alan R. Katritzky
Degenerate ring changes of heterocycles are labeled as reactions during which a heterocyclic procedure is switched over into an analogous hetercyclic procedure. This monograph covers an authoritative, accomplished evaluate of a number of degenerate ring modifications in 5- and 6-membered heterocycles. It indicates how by means of 15N-labeled, 13C-labeled or selectively substituted compounds those degenerate ring trnasformations will be came upon and hwo many of the effects may be defined via the Addition Nucleophile, Ring beginning, Ring Closure [ANRORC] mechanism. one other major topci of the monograph is the occurance of degenerate ring modifications.
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This publication via Kaplan and Vekhter brings jointly the molecular global of the chemist with the condensed subject global of the physicist. ahead of the cave in of the Soviet Union, chemists within the West committed lit to relationships among molecular digital constitution and tle consciousness solid-state vibronic phenomena.
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Whereas for X ϭ SO2C6H5group the ANRORC process occurs for only a relative small percentage, for X ϭ SO2CH3 the ring-opening process is strongly favored. 27). However, it appeared that in the -adduct 48 the SO2CH3 group is present in the deprotonated form. This behavior probably explains why 2-phenylsulfonyl-4-phenylpyrimidine reacts differently from 2-methylsulfonyl-4-phenylpyrimidine. 27). 6). (85T237). For that purpose the Swain nonresonance ﬁeld constants F and resonance constants R were used (68JA4328).
All the results mentioned in this section indicate that the aminolysis of highly activated pyrimidines containing a leaving group at position C-2 or C-4(6), a reaction that is usually considered to take place via an addition–elimination process, can also occur via the less conventional SN(ANORC) mechanism. As an illustration: It is not unlikely that the aminolysis of 2-chloro-4,6-dicyanopyrimidine into 2-amino-4,6cyanopyrimidine with ammonia (77KGS821) may at least partly occur by participation of a SN(ANRORC) mechanism.
In the strong basic medium, this hydrogen is abstracted and a strongly delocalized anion is formed. Evidence for this anion formation is provided by 1H NMR spectroscopy (74RTC237; 75OMR86). It can be argued that in this anion most of the negative charge is localized in the N-1, C-2, N-3 region, making the nucleophilic attack at position 2 less favorable than addition at C-6, because of electron repulsion between the incoming amide ion and the highly charged region around position 2. 30. f. Aminodemethoxylation of Dimethoxypyrimidines It has been reported that 4,6-dimethoxypyrimidine and its 5-bromo derivative undergo an aminodemethoxylation to the corresponding 4-methoxy-6-aminopyrimidines on treatment with potassium amide/liquid ammonia (61JCS1298; 65JCS6659).