Unusual Reactions Between Aromatic Carbon Supernucleophiles and 1,2‐Diazabuta‐1,3‐dienes: Useful Routes to New Pyrazolone and Cinnoline Derivatives

Abstract

Reactions between 1,3,5‐tris(dialkylamino)benzenes and 1,2‐diazabuta‐1,3‐dienes produce semicarbazone derivatives through attack of the supernucleophile aromatic carbon atom at the terminal carbon atom of the heterodiene reagent. The strong activation of the aromatic ring due to the presence of the three amino groups in a symmetrical relationship promotes electrophilic aromatic substitution by the neutral carbon atom of the electrophile. The resulting semicarbazones, in methanol in the presence of sodium methoxide, mainly afford pyrazolone derivatives, whereas in THF in the presence of sodium methoxide an unusual cyclization reaction produces cinnoline derivatives as the major products. Both cyclization reaction mechanisms are discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Cultivating the Passion to Build Heterocycles from 1,2‐Diaza‐1,3‐dienes: the Force of Imagination

“…The formation of cynnolines 59 prevailed mainly in tetrahydrofuran through an intramolecular nucleophilic aromatic substitution involving the displacement of a secondary amino group with loss of the R 1 moiety from intermediates 58 (Scheme 13, Path B). [24] Scheme 13. Synthesis of pyrazolones 57 and cynnolines 59 by reaction of DD 1d,g,h with 1,3,5-tris(dialkylamino)benzene derivatives 54.…”

Phospha‐Michael‐Type Reactions between 1,2‐Diaza‐1,3‐dienes and Bidentate Nucleophiles: Formation of New Mono‐ and Diylides and their Elaboration to Heterocycles

“…Consequently, one can infer that a Zw-like intermediate is a very short-lived species that immediately undergoes a shift of the proton positioned α to three electron-withdrawing groups, a shift furthermore favoured by the presence of the negative charge on the nitrogen atom, as previously observed in analogous systems. [6,20] Finally, we wish to focus attention on an interesting feature found during the NMR monitoring of the course of the reaction between 1a and 2a in CD 2 Cl 2 under variabletemperature NMR conditions. Immediately after the addition of compound 2a to a solution of 1a, cooled to -70°C, the 31 P NMR spectrum showed, together with a small amount of 2a (δ P = -23.5 ppm), two pairs of doublets, at +22.8 and -28.8 ppm (J P,P ≈ 62 Hz) and +20.3 and -27.4 ppm (J P,P ≈ 61 Hz) indicating the presence of two species.…”

“…It is noteworthy that the dynamic process observed is reversible: after warming of the solution from -70°C to room temperature and cooling again to -70°C, 31 P and 1 H NMR spectra identical to the starting one were obtained, thus suggesting the existence of two rotamers at low temperatures. By application of the Eyring equation, [21] these data permitted us to calculate an activation energy of ΔG # = (11.2 Ϯ 0.2) kcal mol -1 for the process, a value consistent [20,22] with that of a rotational constraint due, in this case, to the bulky groups present on compound 3a, which make the molecule quite rigid. It is reasonable to suppose that this phenomenon occurs in all compounds 3 and 4.…”

Zn(II)-Catalyzed Addition of Aromatic/Heteroaromatic C(sp2)–H to Azoalkenes: A Polarity-Reversed Arylation of Carbonyl Compounds

“…With this objective, the transformation of a carbonyl group into a hydrazone functionality ( d 2 -to-a 2 ) represents an intriguing alternative to conventional strategies (Figure ). Realizing the need for a practical and more sustainable catalytic arylation/heteroarylation method, we report herein the first Lewis acid catalyzed addition of activated (hetero)­aromatic C–H substrates (π nucleophiles) to azoalkenes …”