Protic acid-induced intramolecular reactions of 2-cyclopropylazobenzenes

Федотов, А. Н.; Shishkina, I. N.; Kutateladze, Tatiana G.; Mochalov, S. S.; Shabarov, Yu. S.

doi:10.1007/bf00473455

Cited by 4 publications

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“…This hypothesis is supported, for example, by the finding that neither o-nitrophenylcyclopropanes nor o-cyanophenylcyclopropanes rearrange by the action of trifluoroacetic acid, while these compounds are converted quantitatively to the corresponding products of transformation of the three-membered carbocycle by the action of concentrated sulfuric acid [12,18]. It is interesting that phenylcyclopropane lacking electron-withdrawing substituents or phenylcyclopropanes with weak electron-withdrawing substituents in the ortho position [5,14,19] are converted by the action of trifluoroacetic acid, similarly to cyclopropylureas 2a-i, into the corresponding cyclopropane ring transformation products. _______ * Cyclopropane 2a was obtained by the reaction of 2-cyclopropylaniline (1) with potassium cyanate (see Experimental).…”

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confidence: 94%

Synthesis of 2-amino-4H-3,1-benzoxazines and 2-amino-4H-3,1-benzothiazines by the rearrangement of o-cyclopropylphenylureas and o-cyclopropylphenylthioureas

Федотов

Трофимова

Romanov

et al. 2008

Chem Heterocycl Comp

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Syntheses are reported for 2-cyclopropylphenylureas and 2-cyclopropylphenylthioureas and the behavior of these compounds was studied under conditions for the acid-catalyzed opening of the cyclopropyl ring. Upon the action of concentrated sulfuric acid or trifluoroacetic acid, these ureas and thioureas can undergo rearrangement to the corresponding 3,1-benzoxazines and 3,1-benzothiazines.Functionally-substituted cyclopropanes, which have now become readily available, are finding increasing use as starting compounds in the synthesis of various organic compounds produced by the transformation of the three-membered ring upon the action of specific reagents. These transformations may yield either saturated or unsaturated acyclic products of opening of the cyclopropyl ring [1-4] or carbo-and heterocycles [5][6][7][8][9][10][11]. An especially large number of studies have been devoted to donor-acceptor functionally-substituted cyclopropanes [11]. The reactions in this case proceed predominantly with the participation or effect of the substituents directly bound to the three-carbon ring. There has been considerably less work on the transformations of cyclopropane compounds, in which the substituents, not directly bound to the cyclopropane ring, participate in the reaction. Nevertheless, examples of such transformations [9,[12][13][14] show that the synthetic scope of functionally-substituted cyclopropanes may be considerably expanded. Here, definite promise is found in intramolecular acid-catalyzed ortho-substituted arylcyclopropanes due to the unique ortho-orienting effect of the cyclopropane substituent in electrophilic nitration reactions [15][16][17]. These reagents are now readily available.In a search for new examples of the intramolecular rearrangement of ortho-functionally-substituted arylcyclopropanes, we synthesized 2-cyclopropylphenylureas and 2-cyclopropylphenylthioureas and studied their transformations in trifluoroacetic and concentrated sulfuric acids. We assumed that the acid-catalyzed opening of the cyclopropane ring in suitable cyclopropylureas and cyclopropylthioureas would initiate reaction of the resultant benzylic carbenium ion with the internal nucleophile (urea or thiourea fragment) to form 2-amino-3,1-benzoxazines and 3,1-benzothiazines or isomeric compounds. _______ * Deceased. __________________________________________________________________________________________

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confidence: 94%

Synthesis of 2-amino-4H-3,1-benzoxazines and 2-amino-4H-3,1-benzothiazines by the rearrangement of o-cyclopropylphenylureas and o-cyclopropylphenylthioureas

Федотов

Трофимова

Romanov

et al. 2008

Chem Heterocycl Comp

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“…Substituted-2 H -indazoles were prepared by thermal decomposition of 2-azidobenzylideneamines,24 by TiCl 4 -mediated cyclization of 2-arylazophenylacetic acid derived ketene acetal,25 by cyclization of 2-cyclopropylazobenzenes in concentrated sulfuric acid,26 from 2-nitrobenzylamines by electroreduction,27 by reaction of azobenzene with in situ prepared isopropylidenecarbene,28 and SnCl 2 -mediated cyclization of nitro arenes 29. 2-Acylaminoindazoles were prepared via oxidative cyclization of N-acyl hydrazones of 2-aminoaryl ketones 30,31.…”

Section: Introductionmentioning

confidence: 99%

“…Reported synthetic procedures for 2,3-derivatized-2 H -indazoles often required preparation of dedicated intermediates and/or harsh reaction conditions. Substituted-2 H -indazoles were prepared by thermal decomposition of 2-azidobenzylideneamines, by TiCl 4 -mediated cyclization of 2-arylazophenylacetic acid derived ketene acetal, by cyclization of 2-cyclopropylazobenzenes in concentrated sulfuric acid, from 2-nitrobenzylamines by electroreduction, by reaction of azobenzene with in situ prepared isopropylidenecarbene, and by SnCl 2 -mediated cyclization of nitro arenes . 2-Acylaminoindazoles were prepared via oxidative cyclization of N-acyl hydrazones of 2-aminoaryl ketones. , Polyfused heterocycles containing indazole moiety were prepared by palladium-catalyzed cross-coupling reactions. , …”

Section: Introductionmentioning

confidence: 99%

Remarkably Efficient Synthesis of 2H-Indazole 1-Oxides and 2H-Indazoles via Tandem Carbon−Carbon Followed by Nitrogen−Nitrogen Bond Formation

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“…_______ * A cyclopropane fragment, directly bonded to a carbon atom with a complete positive charge, is easily isomerized [36]. It has been shown [24] that 2-cyclopropylazobenzene is capable of rearrangement into 3-ethyl-2-phenyl-2H-indazole under the influence of trifluoroacetic acid, but is unchanged under the influence of formic acid even on heating. With the objective of retaining the three-carbon ring under the conditions of cyclization of the azoalcohol 14k, we carried out the reaction in formic acid.…”

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confidence: 98%

“…It is important to underline that at present a wide range of precursors has been used to synthesize the 2H-indazole ring, in practice including all strategic routes for its synthesis. For example, 2H-indazoles have been synthesized from 2-azidobenzylideneamines [17] or 2-azidobenzoylamines [18,19], oxidative cyclization from N-acylhydrazones of 2-aminoacylbenzenes [20,21], reaction of carbenes with azobenzene [22,23], rearrangement of ortho-substituted azobenzenes [24,25], and reductive heterocyclization of ortho-nitrobenzylideneamines [26][27][28], and heterocyclization of ortho-nitrobenzylamines [29][30][31][32][33]. A variant of the formation of the 2H-indazole system from compounds containing the pyrazole unit have been described.…”

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A new effective route for the synthesis of substituted 2h-indazoles

Mochalov

Khasanov

Трофимова

et al. 2009

Chem Heterocycl Comp

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A two-stage synthesis of 2H-indazoles has been established, based on consecutive reactions of reduction of 2-alkyl-, 2-cyclopropyl-, and 2-arylcarbonylazobenzenes to phenylazo-substituted benzyl alcohols and intramolecular heterocyclization of the reduction products under the influence of organic acids.In recent years there has been a considerably strengthened interest in the synthesis and study of the medicobiological properties of derivatives of 2H-indazoles, resulting from the observation in a series of compounds which are seldom encountered in nature, a class of heterocycles with a wide range of biological activity: antiangiogenic [1], anticarcinogenic and anti-inflammatory [2,3], antimicrobial [4], antifungal [5,6], cytotoxic [7], and antihelminthic [8]. In addition compounds of this class show potential as inhibitors of NO-synthetases [9, 10], protein kinases [11,12], tubulin [13], modulators of X-receptors of the liver [14], and they also show properties of male contraceptives [15,16].The discovery of the biological activity of the 2H-indazoles caused the real problem of the synthesis of new derivatives of this class of heterocycles. It is important to underline that at present a wide range of precursors has been used to synthesize the 2H-indazole ring, in practice including all strategic routes for its synthesis. For example, 2H-indazoles have been synthesized from 2-azidobenzylideneamines [17] or 2-azidobenzoylamines [18,19], oxidative cyclization from N-acylhydrazones of 2-aminoacylbenzenes [20,21], reaction of carbenes with azobenzene [22,23], rearrangement of ortho-substituted azobenzenes [24,25], and reductive heterocyclization of ortho-nitrobenzylideneamines [26][27][28], and heterocyclization of ortho-nitrobenzylamines [29][30][31][32][33]. A variant of the formation of the 2H-indazole system from compounds containing the pyrazole unit have been described. For example, oxidation of 4,5-tetramethylenepyrazoles with dichlorodicyanobenzoquinone gave substituted 2H-indazoles in high yield [34]. However, despite the abundance of variants for the construction of the 2H-indazole ring, the variation of substituents is practically limited to those in positions 2 and 3, and only in the papers [30,31,33] were syntheses of 2H-indazoles containing substituents in the annelated benzene ring reported.

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Protic acid-induced intramolecular reactions of 2-cyclopropylazobenzenes

Cited by 4 publications

References 2 publications

Synthesis of 2-amino-4H-3,1-benzoxazines and 2-amino-4H-3,1-benzothiazines by the rearrangement of o-cyclopropylphenylureas and o-cyclopropylphenylthioureas

Synthesis of 2-amino-4H-3,1-benzoxazines and 2-amino-4H-3,1-benzothiazines by the rearrangement of o-cyclopropylphenylureas and o-cyclopropylphenylthioureas

Remarkably Efficient Synthesis of 2H-Indazole 1-Oxides and 2H-Indazoles via Tandem Carbon−Carbon Followed by Nitrogen−Nitrogen Bond Formation

A new effective route for the synthesis of substituted 2h-indazoles

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