ANRORC

Reactions with strongly basic nucleophiles such as potassium amide in liquid ammonia may prove much more complex than direct substitution. 2-Chloro-4,6,7-triphenylpteridine reacts under these conditions via an S ANRORC mechanism to form 2-amino-4,6,7-triphenylpteridine and the dechlorinated analogue (78TL2021). The attack of the nucleophile exclusively at C-4 is thereby in good accord with the general observation that the presence of a chloro substituent on a carbon position adjacent to a ring nitrogen activates the position meta to the chlorine atom for amide attack. 

In both these ring transformation reactions, the ANRORC troika process takes place [99AHC(74)8]. Usually, however, the action of a nucleophile on 1,2,4-... 

An ANRORC mechanism has also been proposed (besides an inverse cycloaddition reaction) in the conversion of 1-methylpyrimidinium iodide into 3-ethoxycarbonyl-2-methylpyridine on treatment with ethyl -amino-crotonate (95RCB1272) (Scheme 23a). The reaction starts by addition of the -carbon of the crotonate at the electron-deficient 4-position of the... 

In certain cases, the SrnI mechanism has been found (p. 856). When the substrate is a heterocyclic aromatic nitrogen compound, still a different mechanism [the Sn(ANRORC) mechanism], involving opening and reclosing of the aromatic ring, has been shown to take place. 

The amino-debromination of 6-bromo-4-phenylpyrimidine (Scheme 1.3). The reaction has been proved to occur by the formation of an initial ct-adduct at C-2, which subsequently rearranges into the 6-amino product [Sn(ANRORC) mechanism]. 

Sn(ANRORC) Reactions in Azines, Containing an Outside Leaving Group... 

It became evident that the mechanism for the simple hydroxydechlorination replacement reaction decribed in Scheme II.7 occurs in a way very different from the aminodebromination of 2-bromopyridine, but very similar to that of 2-bromopyrimidine (see Section II,C,l,c). It is, however, good to stress the point that, although the aminodehydroxylation occurs according to an Sn(ANRORC) mechanism, it does not involve a degenerate ring transformation. 

In conclusion, the amination of 2-chloro-5-nitropyridine mainly occcurs according to the Sn(ANRORC) mechanism (about 75%) and to a smaller degree (about 25%) according to the Sn(AE) process. 

Amination of 3-bromoisoquinoline with potassium amide/liquid ammonia involves (in contrast to the amination of 2-bromopyridine, see Section an ANRORC process. When 3-bromo[ N]isoquinoline was used as substrate, the 3-aminoisoquinoline being obtained contains 55% of its enrichment on the exocyclic nitrogen, i.e., the formation of 3-[ N-aminoJisoquinoUne (14), and 45% inside the heterocyclic ring, i.e., formation of 3-amino[ N]isoquinoline (13) (74RTC198). 

As we have seen in Section II,A, 6-bromo-4-phenylpyrimidine reacts on treatment with potassium amide in liquid ammonia at -75°C into the corresponding 6-amino compound nearly quantitatively according to the Sn(ANRORC) mechanism (71RTC1239). Extensive investigations have been carried out on the scope and limitations of this mechanism and on the several factors that influence the occurrence of the Sn(ANRORC) mechanism in the aminodehalogenation of 4-substituted-6-halogenopyrimidines. 

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