Read e-book online Advances in Heterocyclic Chemistry, Vol. 74 PDF

By Henk C. van der Plas, Alan R. Katritzky

ISBN-10: 0120207745

ISBN-13: 9780120207749

Degenerate ring variations of heterocycles are categorized as reactions within which a heterocyclic approach is switched over into an analogous hetercyclic process. This monograph covers an authoritative, accomplished assessment of a bunch of degenerate ring modifications in 5- and 6-membered heterocycles. It exhibits how via 15N-labeled, 13C-labeled or selectively substituted compounds those degenerate ring trnasformations will be came upon 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 differences.

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One possible reason that in 6-X-4-phenylpyrimidine the addition at C-2 is so favored has to do with steric effects: Addition at C-4 is hampered by the bulky phenyl group, and addition at C-6 by the halogeno atom. 20A). It has also been postulated that the addition of the amide ion at C-2 is possibly favored by metal complexation of potassium amide with the azomethine bond between N-3 and C-2 (see transition state 35), because of more basic character of N-3 ( para toward X) compared to N-1 (ortho toward X).

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).

These results strongly indicate that the addition is an orbital-controlled reaction. One possible reason that in 6-X-4-phenylpyrimidine the addition at C-2 is so favored has to do with steric effects: Addition at C-4 is hampered by the bulky phenyl group, and addition at C-6 by the halogeno atom. 20A). It has also been postulated that the addition of the amide ion at C-2 is possibly favored by metal complexation of potassium amide with the azomethine bond between N-3 and C-2 (see transition state 35), because of more basic character of N-3 ( para toward X) compared to N-1 (ortho toward X).

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


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