Uncommon Heterocyclization into a Pyrazole System of Z-3-(2-Naphthyl)-3-chloro-2-propenal Semicarbazone and Thiosemicarbazone

Abstract

By reaction of Z-3-(2-naphthyl)-3-chloro-2-propenal with semicarbazide hydrochloride and thiosemicarbazide the corresponding semicarbazone and thiosemicarbazone were obtained that underwent a heterocyclization into a pyrazole system with elimination of amide moieties and with migration of the naphthyl fragment into the position 4 of the pyrazole ring. The alkylation of 4-(2-naphthyl)pyrazole synthesized with 2-nitropentachloro-1,3-butadiene afforded 1,1-bis[4-(2-naphthyl)-pyrazol-1-yl]-2-nitrotrichloro-1,3-butadiene.Z-3-(2-Naphthyl)-3-chloro-2-propen-1-al (I) easily prepared from 2-acetonaphthone by VilsmeierHaack reaction [1] contains two reactive sites (C=O and =CCl) that permits an effective application of the compound to building up versatile heterocyclic systems including a naphthalene fragment: benzodiazepine, isoxazole, pyrimidine [2], and quinoline [3]. We formerly demonstrated that the reaction between chloropropenal I and hydrazine hydrate was a convenient procedure for preparation of 5-(2-naphthyl)pyrazole [2].The goal of this study was preparation of chloropropenal I semicarbazone and thiosemicarbazone and the attempt at their heterocyclization into a pyrazole system containing a naphthalene fragment and amide or thioamide groups respectively.Semicarbazone II and thiosemicarbazone III of chloropropenal we obtained in 8082% yield by reacting chloropropenal I with semicarbazide hydrochloride and thiosemicarbazide respectively. The IR spectra of compounds II and III obtained lacked the absorption bands of the aldehyde group and contained the bands from C=N bonds vibrations at 1563 (compound II) and 1597 cm 1 (compound III). Vibrations of the NH 2 groups of compounds II and III are characterized by absorption bands at 3473 and 3432 cm 1 respectively, and vibrations of the NH groups appeared as broadened bands in the region 32063283 cm 1 . In the 1 H NMR spectra of compounds II and III alongside the resonances from the protons of the naphthyl groups and exocyclic =CH broadened singlets were observed with the chemical shifts d 9.410.5 and 6.356.45 ppm belonging to the protons of the NH and NH 2 groups respectively.The heterocyclization of compounds II and III into a pyrazole system was effected by boiling in the glacial acetic acid. We expected to obtain pyrazole with a naphthyl fragment attached to position 5 of the ring and amide or thioamide group in position 1. However the process occurred differently and involved a loss of amide groups and a migration of the naphthyl fragment into position 4 of the pyrazole ring. Thus in both cases the same product was obtained that based on elemental analysis, 1 H NMR, IR, and mass spectra was assigned a structure of 4-(2-naphthyl)pyrazole (IV).In the mass spectrum of compound IV the molecular ion peak is present with m/z 194 and relative abundance 100%, and the elemental analysis corresponds to an empirical formula C 13 H 10 N 2 . The IR and 1 H NMR spectra of compound IV essentially differ from the spectra of 5-(2-naphthyl)-pyrazole (V) we have synthesized p...

Chemistry of Polyhalogenated Nitrobutadienes, Part 7: A Novel Synthetic Access to Chlorinated Nitrile Oxides

“…Due to its stepped reactivity, 2-nitroperchlorobuta-1,3-diene (1) has proved a valuable synthetic building block for heterocycles via S N Vin reactions. [1][2][3][4] Substitution with two equivalents of primary N-nucleophiles such as aniline and its electron-rich derivatives 2 (ERG = electron-releasing group) leads to the formation of ketene aminals 3, probably via the corresponding amidines. 5 On the contrary, during reaction with electron deficient anilines 4 (EWG = electron-withdrawing group) such as 4-nitroaniline a different reaction channel is opened instead after the first N-substitution, leading to allylidene arylhydrazines 5 (Scheme 1).…”

Synthesis of Diheteroatomic Five‐Membered Heterocyclic Compounds from α,β‐Unsaturated Aldehydes

“…Substituted 2‐alkenals 66 , which contained an easily eliminated nucleophilic group at the 3‐position, have been employed as a scaffold for the construction of pyrazoles ,. Over the past 10 years, it has been shown that the reaction of 3‐dimethylamino‐5‐(trimethyl‐2‐cyclohexen‐1‐yl)‐2,4‐pentadienal ( 66 a ) or 3‐chloro‐3‐(2‐naphthyl)‐propenal ( 66 b ) with hydrazine hydrate ( 67 c ) readily furnishes the corresponding 1H‐pyrazoles ( 69 ) in 89 and 74 % yield, respectively. The reaction proceeds through a hydrazone intermediate ( 68 ), which cyclizes by nucleophilic vinyl substitution of the chlorine atom or the dimethylamino moiety.…”