Nucleophilic heteroaromatic

Vn. Appendix Kinetic Data for Nucleophilic Heteroaromatic Substitution. 359... 

One of the merits of the above treatment, which justifies its inclusion in this review, is that it allows a quantitative comparison of the selectivity of nucleophilic heteroaromatic substitution (expressed by the reaction constant) with that for the analogous reaction with nitro-activated systems. Values for the latter are in the range 3.6 to 6.0. The fact that in both cases high p-values of similar magnitude are found is consistent with the hypothesis of similar mechanisms for both classes of compounds. 

Fig. 7. Potential-energy diagrams for nucleophilic heteroaromatic substitutions. A, solid line very probable and common B, solid line probable but less frequent A and B, dotted lines scarcely probable and/or infrequent.

Balli and Felder (1978) and Balli and Ritter (1981) showed that diazo transfer can be applied advantageously to the diazotization of sufficiently nucleophilic heteroaromatic compounds such as 5-hydroxy- and 5-amino-3-methyl-l-phenyl-pyrazole if 3-ethyl-2-azido-benzthiazolium tetrafluoroborate (2.50) is used as diazo transfer reagent (for other applications of this diazo transfer reagent see Zollinger, 1995, Secs. 2.6-2.8). The diazonio group is introduced in the 4-position (2.51). 

Pyrazolo[l,5-A benzisothiazoles 252 were prepared from 3(5)-[2 -methyl-thiophenyl]pyrazoles 251 and AT-chlorosuc-cinimide. The ring closure may involve a sequential nucleophilic heteroaromatic nitrogen displacement of a sulfonium chlorine atom followed by dealkylation of the resulting sulfonium salt to form the sulfenylimine moiety (Equation 110) <1996H(43)221>. 

There is a limited number of examples of preparations involving the reaction of stannyl-alkali metal compounds with a substituted heteroarene, for example, Equations (58)-(60).88,197,198 Some of these reactions (e g Equation (58)) occur only with photoirradiation, showing that they involve SRN1 processes, but others may be straightforward nucleophilic heteroaromatic substitutions. 

A survey of the quantitative studies on nucleophilic heteroaromatic substitution1 disclosed a complete lack of information on heterocyclic... 

Other solvents also are not inert to the alkylating agent. For example, DMSO and Mel react, first (reversibly) at oxygen and then at sulfur.45 This side-reaction becomes important only in quaternization studies involving poorly nucleophilic heteroaromatic substrates.41... 

Research in the Department of Chemistry of the School of Pharmacy of the University of Bari Nucleophilic Reactivity of Aromatic Derivatives, and Synthesis and Reactivity of Heterocyclic Derivatives P. E. Todesco, Corsi Semin. Chim., 1968, 50-53. Nucleophilic Heteroaromatic Substitution G. Illuminati, Adv. Heterocyclic Chem., 1964, 3, 285-371. 

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