Reactions of the ambident super-electrophile series: the 2-(nitroaryl)-4,6-dinitrobenzotriazole 1-oxides with isopropoxide ion. Pathways of decomposition of the anionic σ-adducts

Abstract

This paper is dedicated to Professors David B. McLeatz and Ian D. Spenser JULIAN M. DUST and ERWIN BUNCEL. Can. J. Chem. 72,218 (1994). To elucidate the reactivity of super-electrophiles such as 4,6-dinitrobenzofuroxan as compared to normal electrophiles such as 1,3,5-trinitrobenzene, reaction of isopropoxide ion (iPrO-) with a series of ambident super-electrophiles was studied by 400 MHz 'H nuclear magnetic resonance spectroscopy. The 2-(nitroary1)-4,6-dinitrobenzotriazole l-oxides, 1-3, possess both a super-electrophilic (C-7) site and a normal electrophilic (C-1') site. Nucleophiles can demonstrate selectivity for attack at C-7, which leads to formation of persistent anionic u-adducts (Meisenheimer complexes), as compared to C-1', which leads to N-2:C-1' bond scission. The most reactive substrate, 2-(2',4',6'-trinitrophenyl)-4,6-dinitrobenzotriazole l-oxide (Pi-DNBT, 1) was found to be the least selective substrate in C-7 adduct formation, while 2-(2',4'-dinitrophenyl). and 2-(4'-nitropheny1)-4,6-dinitrobenzotriazole l-oxides (DNP-DNBT, 2, and NP-DNBT, 3, respectively) showed increasing selectivity towards iPrC-, in turn. These results are discussed on the basis of overall selectivity for C-7 adduct formation and the relative selectivity of iPrO-as compared to methoxide and tert-butoxide ions. The conclusions are illustrated using comparative energy profiles. In terms of pathways for decomposition of the adducts, the C-7 adducts decompose via dissociation back to substrate and nucleophile and, thence, through C-1' adduct formation to the scission products. However, for 1, the C-7 adduct l a has now been found to decompose to 7-isopropyl-2-picryldinitrobenzotriazole, lc. The possible mechanism of this formal internal redox will be discussed. Chem. 72,218 (1994). Afin d'tvaluer la rCactivitC des super-Clectrophiles, comme le 4,6-dinitrobenzofuroxane, par rapport a celle d'tlectrophiles normaux, comme le 1.3,s-trinitrobenz&ne, on a utiliser la resonance magnCtique nuclkaire du 'H ? I 400 MHz pour ttudier la rCaction de l'ion isopropylate (iPrC-) avec une sCrie de superClectrophiles ambidents. Les 2-(nitrowl)-4,6-dinitrobenzotriazole l-oxydes, 1-3, posskdent un site superClectrophile (C-7) ainsi qu'un site Clectrophile normal (C-l').Les nucltophiles permettent de dtmontrer une sClectivitC pour l'attaque en C-7 qui conduit a la formation d'adduits u anioniques persistants (complexes de Meisenheimer) alors que I'attaque en C-l'conduit a une scission de la liaison N-2:C-1' . On a trouvC que le substrat le plus rkactif, la 2-(2',4',6'-trinitrophCnyl)-4,6-dinitrobenzotriazole I-oxyde (Pi-DNBT, I), est le substrat le moins stlectif pour la formation d'un adduit en C-7 alors que les 2-(2',4'-dinitrophCny1)-et 2-(4'-nitrophCny1)-4,6-dinitrobenzotriazole l-oxydes (respectivement la DNP-DNBT, 2, et NP-DNBT, 3) prCsentent chacune une sClectivitC de plus en plus grande vis-a-vis du iPrO-. On discute de ces rksultats en fonction de la sClectivitC globale de la formation d'adduits en C-7 et la sClectivitC relative du iPrO-comp...

The ambident electrophilic behavior of 5‐nitro‐3‐X‐thiophenes in σ‐complexation processes

“…Most importantly, carbon C‐2 of thiophene 1 exhibits an electrophilicity ( E = –13.42) that compares well with that of 1,3,5‐trinitrobenzene 18 ( E = –13.19), the common reference aromatic electrophile in nucleophilic addition processes …”

“…On the other hand, these data reveal that thiophene 2 displays an electrophilicity reactivity at C-2 positions (E = -16.48) that compares well with that of 2,5- Most importantly, carbon C-2 of thiophene 1 exhibits an electrophilicity (E = -13.42) that compares well with that of 1,3,5-trinitrobenzene 18 (E = -13.19), the common reference aromatic electrophile in nucleophilic addition processes. 35,[59][60][61][62]…”

Ambident reactivity of aryloxide ions towards the super-electrophile, 4,6-dinitrobenzofuroxan. Kinetics, thermodynamics and stereoelectronic factors on regioselectivity

“…This decomposition, in which the sp 3 -bound proton (H-7) of the adduct is transferred to the 1-oxide oxygen which may subsequently be lost, has been observed previously as a competitive process in the reaction of methoxide with NBF 23 and in the reaction of Pi-DNBT with isopropoxide ion. 24 In the case of the NBF and TNB reactions with 3,5-DTBPhO Ϫ , however, the aryloxide O-adducts could be seen and their structural features assigned using the low temperature medium (MeCN-DME).…”