Reactivity parameters, indole

The series of para-substituted 2-ary 1-1,3-dithianyl carbanions shown in Table 6 and equation (41) are expected to differ in LUMO energy. The phenoxide-substituted anion (entry 1, Table 6 and equation 41) should have higher LUMO relative to, for example, the simple phenyl-substituted anion (entry 6) and gives a greater preponderance of meta substitution due to stronger orbital control. The smooth correlation of selectivity with reactivity for this series of closely related anions is consistent with a simple two-parameter analysis. Other regioselectivity results, such as those with o-alkylanilines (Table 2 and equation 30) and [(indole)Cr(CO)3] also have been analyzed in terms of orbital control and conformational effects.87,88,93... 

Sevilla MD, Becker D, Mengyayo Y (1990b) Structure and reactivity of peroxyl and sulphoxyl radicals from measurement of oxygen-17 hyperfine couplings relationship with Taft substituent parameters. J Chem Soc Faraday Trans 86 3279-3286 Shen X, Lind J, Eriksen TE, Merenyi G (1989) The reaction of the CCI3O2 radical with indoles. J Chem Soc Perkin Trans 2 555-562... 

Dinitrobenzofuroxan (DNBF) is known as a superelectrophile due to its high reactivity both as an electrophile and in its pericyclic addition reactions. NMR studies show that reaction with 2-aminothiazole and its 4-methyl derivative yield anionic carbon-bonded adducts such as (11) by reaction at the 5-position, whereas the 4,5-dimethyl derivative reacts via the exocyclic amino group. Kinetic studies of the first two compounds, both in acetonitrile and in 70 30 (v/v) water-DMSO, have been used to assess their carbon nucleophilicities and place them on the Mayr nucleophilicity scale.55 In a related study, the nucleophilic reactivity, in acetonitrile, of a series of indoles with both DNBF and with benzhydryl cations have been compared and used to determine nucleophilicity parameters for the indoles.56... 

The scope of this reaction is limited to electron-rich arenes and heteroarenes such as thiophenes, pyrroles, furans, indoles, and alkoxybenzenes as nucleophilic partners, corresponding to a Mayr ir-nucleophilicily parameter N>-1 [75-78], Electron-neutral to electron-deficient iodo(hetero)arenes are suitable electrophilic partners. Aryl halides or pseudohalides that are less reactive towards oxidative addition (Br, Cl, OTf) are not sufficiently reactive partners in this reaction. The reactivity of sterically hindered and/or ortho substituted iodoarenes has not been demonstrated. However biaryls bearing one ortho substituent of relatively small steric demand (e.g., from methoxybenzene or /V-mcthylindole) have been prepared. 

Calculations of ru-electron densities of indole using the Huckel method, when appropriate parameters are introduced into the calculation to take into account the electronegativity of the nitrogen atom, give a 7i-density order of3>2>4 5 6 7 (57). The method employed predicts correctly the order of positional reactivity of the pyrrole ring, whereas it has not predictive value for positions in the benzene ring. 

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