Superelectrophilic heterocycles: facile S_NAr–S_EAr couplings involving very weak carbon nucleophiles

Abstract

Superelectrophilic halonitro-2,1,3-benzoxadiazoles undergo remarkably facile carbon-carbon couplings with some electron-rich aromatics and heteroaromatics, affording quantitatively products exhibiting an intense visible absorption due to strong intramolecular charge transfer.

Evidence for the Intermediacy of Wheland–Meisenheimer Complexes in SEAr Reactions of Aminothiazoles with 4,6‐Dinitrobenzofuroxan

“…It remains the case that the most important finding of this work is the successful characterization of WM‐ 1 a by NMR. While it has long been postulated that S N Ar–S E Ar couplings between electron‐rich and electron‐deficient aromatics or heteroaromatics must involve the initial formation of a Wheland–Meisenheimer complex,22–24 only one example in which such an intermediate had a lifetime significantly sufficient to be observed spectroscopically has so far been reported8. Interestingly, this example deals with the reactivity of DNBF–‐a superelectrophilic structure—towards supernucleophilic 1,3,5‐tris‐( N , N ‐dialkylamino)benzenes 26 a – c as shown in Scheme 8.…”

Nucleophilic Reactivities of Azulene and Fulvenes

“…To the best of our knowledge, so far only one system has been reported that addresses this question. Terrier and coworkers determined [21] a second-order rate constant of 5.88  -1 s -1 (MeCN, 25°C) for the reaction of 4,6-dinitrobenzofuroxane with azulene (1). From the electrophilicity parameter of this electrophile (E = -5.06) [20] and the N and s values of 1 given in Table 2, we calculated k 2 as 42.9  -1 s -1 at 20°C.…”

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

“…In order to explain the above observation about reaction rates, one must take into account that (i) the benzofurazan ring has a stronger inductive effect and a lower resonance effect than a nitro group [50]; (ii) the combined result for the nitrobenzofurazan is a strong electron-withdrawing effect facilitating the S N Ar substitution; (iii) methoxy and aryloxy substituents appear to be better leaving groups than chloro; and (iv) there is a transition state leading to the immediate formation of a red-colored Meisenheimer complex 4 [51][52][53][54][55] and then, more slowly, to the substitution product 3 that is detectably fluorescent. One may assume that the basic AAs, which are more nucleophilic than all other AAs, prevail whenever the aryloxy group is not activated (2a) or deactivated by an electronwithdrawing formyl group (2d), even when there are methoxy groups (2e).…”