Reaction of 1-(Chloroalkyl)-1-aza-2-azoniaallene Salts with Alkenes: Preparation of Cyclic Azo, (Azoalkyl)azonium, and Formazanium Compounds

Abstract

a,a -Dichloroazo compounds 9 react with antimony pentachloride to furnish 1-(chloroalkyl)-l-aza-2-azoniaallene salts 10 as reactive intermediates, which are intercepted as 3H-4,5-dihydropyrazolium salts 11 by reaction with electron-rich alkenes. Hydrolysis of salts 11 affords 3H-4,5-dihydropyrazoles 12. 1-Aza-2-azoniaallene salts 1 react with cyclic azoalkanes 12 to produce the N-(azoalkyl)diazenium salts 14 or the formazanium salts 15 depending on the substituents of the starting materials. The structure of 15c is secured by X-ray structural analysis.Recently, we reported the preparation and reactions of 1aza-2-azoniaallene salts 1, a new class of heterocumulenes. Cations 1 were found to undergo cycloadditions to many types of multiple bonds (alkenes, alkynes, nitriles, isocyanates, carbodiimides) affording heterocyclic salts 2, which in most cases rearrange spontaneously to salts 3 and/or isomers (Scheme 1). 1-6 Experimental and theoretical arguments had been advanced suggesting that cycloadditions of 1 to nitriles, isocyanates, as well as to carbodiimides are two-step reactions via nitrilium, and acylium intermediates, respectively. However, cycloadditions of 1-aza-2-azoniaallene cations 1 to C=C double bonds were found to proceed with complete conservation of the configuration of the alkenes. These reactions are probably concerted "1,3-dipolar cycloadditions with reverse electron demand" with 1 serving as a cationic threecenter, four-electron component (1,3-dipole) and the electron-rich alkene as dipolarophile. 3 Similarly, reactions of 1 with alkynes seem to be single-step reactions. 4 Little if any seems to be known about cationic organic 1,3-dipoles. 7Cycloadditions of 1 suffer from the disadvantage that one ends up with salts. For applications, electrically neutral heterocycles would be more desirable. In order to circumvent this problem we tried to prepare heterocumulenes 1 substituted with a leaving group R 3 (e.g. CO 2 Et), which can finally be removed from the cycloadducts 2 and 3. For instance, nitriles can be added to heterocumulenes 4 to afford the carbamates 6, which can be hydrolyzed under mild basic conditions to the triazoles 7. 3 However, it turned out that the reactivity of 4 is rather low, obviously due to the equilibrium 4 s 5. 8,9 Thus cycloadditions of 4 could neither be induced with alkenes nor with alkynes or isocyanates.Better reactivity is observed for heterocumulenes 1 with R 3 = tert-butyl. During or after formation of the cycloadducts 2 and 3 the tert-butyl group is eliminated as isobutene, leaving back a protonated heterocycle, from which the neutral compound can be obtained with base. 3 However, in some cases the elimination of isobutene was difficult to achieve. 5 In other cases preparation of the starting tert-butyl hydrazones proved to be unsatisfactory.In search of 1-aza-2-azoniaallene salts 1 with a more suitable leaving group R 3 , we came across a,a¢-dichloroazo compounds 9 (Scheme 2). Compounds 9 are prepared almost quantitatively by chlorination of azines 8 under mild co...

Synthesis of 3′‐1,2,4‐triazolo‐ and 3′‐1,3,4‐thiadiazoliminothymidines

“…Acetylation of 8 with acetic anhydride in dry pyridine afforded 5 -acetate 9 as a colorless foam in 73% yield. The ␣,␣-dichloroazo compound 4a [25] was obtained by chlorination of the bis-hydrazone, and the 1-aza-2-azoniaallene salt 5a [26,27] by the treatment of 4a at −60…”

Synthesis and Antiviral Activity of 1-[(1,5-Dialkyl-1H-1,2,4-triazol-3-yl)methyl]thymines

“…Treatment of 1 with SbCl 5 at -60 °C gave the intermediates 2 [3,4] which underwent cycloaddition with 1-(cyanomethyl)-thymine 3 [5] . The reaction proceeded at -60 °C for 1 h and then at r.t. for 18 h to give the 1,2,4-triazolium hexachloroantimonates 4.…”

“…The reaction proceeded at -60 °C for 1 h and then at r.t. for 18 h to give the 1,2,4-triazolium hexachloroantimonates 4. The salts 4 rearranged spontaneously by migration of the alkyl group at C-3′′, via [1,2-shift] [3] to N-2′′, accompanied by elimination of the CClR 1 R 2 group at N-1′′, leading to the protonated 1,2,4-triazolomethylthymine derivatives 5. In situ hydrolysis of 5 with aqueous NaHCO 3 afforded the title compounds 6a-c in 87, 66, and 76% yield, respectively.…”

New benzylpiperazine derivatives bearing mono‐ and bis‐dialkyl substituted 1,2,4‐triazoles

“…Recently, the 4,5-dihydro-3H-pyrazolium salts have been synthesized from the cycloaddition of the short-lived 1-(chloroalkyl)-1-aza-2-azoniaallene hexachloroantimonates 3 [25][26][27] to various electronrich alkenes in the presence of Lewis acids like SbCl 5 ; similarly numerous compounds of 1,2,4-triazoles were prepared recently in our laboratory via the cycloaddition of the nitrile derivatives to intermediates 3. Such examples of our recent work are 1,2,4-triazole C-nucleosides [28,29], acyclic C-nucleosides [30], pyrimidines [31], N-alkylphthalimides [32], Dmanno-pentitol-1-yl-1,2,4-triazoles [33], 1H-indoles as well as quinolines [34], benzotriazoles [35], 3 -triazolothymidines [36], N,N -trisubstituted 1,2,4-triazolo-piperazines [37], and 1,2,4-triazole derivatives of acetic acid alkylidene hydrazides [38].…”