105563-83-5Relevant academic research and scientific papers
Ambident reactivity of aryloxide ions towards the super-electrophile, 4,6-dinitrobenzofuroxan, Kinetics, thermodynamics and stereoelectronic factors on regioselectivity
Buncel, Erwin,Manderville, Richard A.,Dust, Julian M.
, p. 1019 - 1026 (1997)
Reactions of the aryloxide ions, phenoxide (PhO-) and 3,5-di-fert-butylphenoxide (3,5-DTBPhO-), with the super-electrophilic heteroaromatic substrate, 4,6-dinitrobenzofuroxan (DNBF, 1), have been examined by 400 MHz 1H NMR spectroscopy in acetronitrile-dimethoxyethane ([2H3]MeCN:[2H10]DME 1:1, v/v) as a function of varying temperature (-40 to 23°C) and in dimethyl sulfoxide ([2H6]DMSO) at room temperature. We herein report the first observation and full characterization of the O-bonded σ-adduct (DNBF·OPh-, 3a) formed by attack of PhO-, acting as an O-nucleophile, at the C-7 super-electrophilic site of 1. No C-5 adduct was seen in the initial spectrum (- 40°C, [2H3]MeCN:[2H10]DME) or in subsequent monitoring of the reaction. These results suggest that PhO- displays K7T7 regioselectivity towards DNBF wherein attack at the C-7 site is favoured by both kinetics and thermodynamics, comparable to the behaviour shown by PhO- towards 2,4,6-trinitroanisole where the C-1 adduct is the product of both kinetic and thermodynamic control (i.e. K1T1 regioselectivity). Upon warming the reaction mixture to ambient, the C-7 O-adduct, DNBF·OPh-, 3a, gives way to the more stable C-7 C-bonded σ-adducts (DNBF-ortho-PhOH- adduct, 4, and DNBF·para-PhOH- adduct, 5, in a ratio of ca. 1:6). The C-7 hydroxide adduct, DNBF-OH- , 2a, and phenol are detected at this temperature. The C-adducts, 4 and 5, are the sole PhO- adducts previously observed in the DNBF-PhO- reaction system (in [2H6]DMSO at room temperature). When C-attachment is precluded by steric hindrance, as in the reaction of 1 with 3,5-DTBPhO-, the C-7 DNBF·OPhDTB- adduct, 3b, is observed by 1H NMR spectroscopy even in [2H6]DMSO under ambient conditions. The results of the kinetics and thermodynamics of aryloxide adduct formation with DNBF, including the ambident reactivity found, are discussed with regard to stereoelectronic stabilization in the adducts and with comparison to relevant 4-nitrobenzofuroxan (NBF), 2-(nitroaryl)-4,6-dinitrobenzotriazole 1-oxides (2-Ar-4,6-DNBT) systems and to the normal electrophile, 1,3,5-trinitrobenzene (TNB).
Reactivity-Selectivity Relationships in Reactions of Ambident Nucleophiles with the Superelectrophiles 4,6-Dinitrobenzofuroxan and 4,6-Dinitro-2-(2',4',6'-trinitrophenyl)benzotriazole 1-Oxide
Buncel, Erwin,Renfrow, Richard A.,Strauss, Michael J.
, p. 488 - 495 (2007/10/02)
The reactions of 4,6-dinitrobenzofuroxan (1) and 4,6-dinitro-2-(2',4',6'-trinitrophenyl)benzotriazole 1-oxide (2) with aryl oxides and arylamines have been investigated.Phenoxide ion reacted with 1 to give a carbon-bonded adduct by reaction at C-7, but in contrast with the 1,3,5-trinitrobenzene (TNB) system, aniline reacted to give both nitrogen- and carbon-bonded adducts as observable species, depending on the reaction conditions.Reaction of 2 with phenoxide ion gave products arising solely from nucleophilic attack at C-1' of the picryl moiety.Reaction of 2 with aniline also yielded a nitrogen-bonded adduct when carried out in the presence of 1 equiv of triethylamine as catalyst.Inhibiting the reactivity of aniline through ortho or N-methyl substitution resulted in the formation of C-7 carbon-bonded adducts of 2.These reactions generally involve kinetically preferred but reversible formation of a ? complex that is bonded via the heteroatom, followed by conversion to a carbon-bonded product of thermodynamic control.The extent to which the kinetically and thermodynamically preferred products can be observed is rationalized according to reactivity-selectivity arguments.The formation of carbon-bonded aniline complexes with 1, but not with TNB, is a result of the greater reactivity of the former (a superelectrophile).The observed regiochemistry in the reaction of nucleophiles with 2 depends on the stability of the adduct at the benzotriazole moiety (C-7) and the selectivity of the nucleophile for reaction at the benzotriazole (C-7) vs. the picryl moiety (C-1').Decreased selectivity will result from an increase in thermodynamic driving force for the addition reaction (more negative ΔG0) and/or, for exergonic reactions, a decrease in intrinsic barrier (i.e., decreased ΔG0(excit.)).Decreased selectivity resulting from decreased intrinsic barriers will favor rapid formation of the products of thermodynamic control.Previous results with related systems are also rationalized on the basis of stability-selectivity relationships.
