Schiff Bases Derived from 6-Amino-2H-chromen-2-one. Synthesis and 1H NMR Spectra

Abstract

A number of 6-arylmethylideneamino-2H-chromen-2-ones were synthesized by reaction of 6-amino-2H-chromen-2-one with aromatic and heterocyclic aldehydes. A linear relation was revealed between the chemical shifts of the azomethine CH=N proton and protons in the chromene ring, on the one hand, and Hammett constants σ of the para substituents, on the other. Formation of intramolecular hydrogen bond in ortho-hydroxy derivatives induces a downfield shift of signals from protons in positions 3-5, 7, and 8 and CH=N proton (9-H) and upfield shift of the o-H signal (14-H). I, R 3 = Et 2 N; II, R 3 = Me 2 N; III, R 3 = HO; IV, R 3 = EtO; V, R 3 = MeS; VI, R 3 = Et; VII, R 3 = AcNH; VIII, R 3 = 5-carboxy-1-methylpyrazol-3-yl; IX, R 3 = BzO; X, R 3 = H; XI, R 3 = Cl; XII, R 3 = Br; XIII, R 3 = CN; XIV, R 3 = O 2 N; XV, R 1 = HO; XVI, R 1 = EtO; XVII, R 1 = F; XVIII, R 1 = Cl; XIX, R 1 = O 2 N; XX, R 1 = R 3 = Me; XXI, R 2 = R 3 = R 4 = MeO; XXII, R 2 = MeO, R 3 = HO; XXIII, R 2 = MeO, R 3 = PrO; XXIV, R 2 = MeO, R 3 = BzO; XXV, R 2 = MeO, R 3 = p-FBzO; XXVI, R 1 = MeO, R 4 = Br; XXVII, R 1 = HO, R 2 = R 4 = Cl; XXVIII, R 2 = O 2 N; XXIX, R 2 = O 2 N, R 3 = Cl; XXX, R 1 = Cl, R 4 = O 2 N; XXXI, R 1 = F, R 5 = Cl; XXXII, R 2 = MeO, R 3 = 5-carboxy-1-methylpyrazol-3-yl; XXXIII, X = 2-hydroxy-1-naphthyl; XXXIV, X = 9-anthryl; XXXV, X = 3-pyridyl; XXXVI, X = 2-hydroxy-6-methylquinolin-3-yl; XXXVII, X = 2-methylindol-3-yl; XXXVIII, X = 1,2-dimethylindol-3-yl; R i = H unless otherwise stated.Compounds of the coumarin series are fluorescent dyes and materials for dye lasers [1-4]. These compounds include N-arylmethylidene derivatives (Schiff bases) of 6-amino-2H-chromen-2-one, which were reported by us previously [5]. In order to study in detail their spectral parameters with regard to the nature of substituent in the arylmethylidene fragment, we have synthesized a number of new Schiff bases belonging to this series.Compounds І-XXXVIII were obtained by condensation of the corresponding aldehydes with 6-amino-2H-chromen-2-one in anhydrous alcohol or dioxane in the presence of a catalytic amount of piperidine on heating for 6 h under reflux. 6-Arylmethylideneamino-2H-chromen-2-ones І-XXXII were synthesized from substituted benzaldehydes, and Schiff bases XXXIIІ-XXXVIII, from polycyclic and heterocyclic aldehydes. The products were isolated and purified by standard procedures. They were yellow to orange crystalline substances. The structure of compounds І-XXXVIII was confirmed by the 1 H NMR spectra (see Experimental), and physical constants of previously described compounds ІI, III, X, and XV coincided with published data [5][6][7]. The 1 H NMR spectra of the newly synthesized compounds were recorded from 0.08 M solutions in DMSO-d 6 at 25°C. It seemed to be reasonable to compare their spectral parameters (i.e., chemical shifts and coupling constants) and correlate these parameters with their structure, specifically with the nature of R 1 -R 5 substituents in the phenyl ring. 8 7 6 5 O 3 4 O N 9 14 13 12 11 10 R 5 R 1 R 2 R 3 R 4

Synthesis, antitumor activity evaluation, and DNA‐binding study of coumarin‐based agents

“…For the condensation reaction to access Schiff's bases (imines) 4a–f , substituted benzaldehydes with variant electronic effects were employed to be compared with the un‐substituted parent 4a according to the literature . In order to study the effect of changing the electronic environment of the synthesized imines, electron donating (OCH 3 ) derivatives were synthesized to be evaluated against the reported analogues with an electron‐withdrawing group (Cl) 4c and the unsubstituted 4a .…”

Peculiarities of NMR 1Н spectra of 5-arylsulfonyl-1,5-diphenyl-1-penten-3-ones

“…таблицю). Для сигналів о-протонів (2-Н) арилсульфонільного фрагмента, що зв'язаний з метиновою групою, також існує деяка відмінність, однак вона є в межах похибки[8]. Для проведення кореляційних залежностей використовували різні кореляційні константи : константи Гаммета  + та п, які характеризують загальний полярний ефект (<0 -електронодонорний та >0 -електроноакцепторний), що чинить замісник Х на реакційний центр в пара-положенні стосовно незаміщеної сполуки, де Х=Н; константи Окамото-Брауна п + , які враховують ефекти спряження за участю замісника Х; константи R, що є мірою полярного ефекту замісника Х (ефект поля); константи і, що характеризують індукційний вплив замісника та константи Ф, які використовують для визначення кореляційних співвідношень для сполук, що містять гетероелементи, які не є реакційним центром.…”