Chemical Transformations Induced by Triflic Anhydride

Baraznenok, Ivan L.; Nenajdenko, Valentine G.; Баленкова, Е. С.

doi:10.1016/s0040-4020(00)00093-4

Cited by 224 publications

(125 citation statements)

References 253 publications

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“…9 In continuation of our research on acylation reactions 10 and application of Tf 2 O in organic reactions, 11 herein we report the para-acylation of phenols with carboxylic acids in the presence of Tf 2 O (Scheme 1).…”

mentioning

confidence: 87%

Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Khodaei¹,

Nazari²

2011

Bulletin of the Korean Chemical Society

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mentioning

confidence: 87%

Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Khodaei¹,

Nazari²

2011

Bulletin of the Korean Chemical Society

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“…[7] Second, it has been established by Stang and co-workers that triflic anhydride could indeed act as an oxidizing agent, especially towards thiourea and activated ketones, to give isolable dimeric cationic species. [8,9] One of the possible mechanisms suggested by these authors might be especially meaningful as far as the present transformation is concerned: the transfer of an electron from thiourea to triflic anhydride might lead to one equivalent of triflate (CF 3 SO 3 À ) and one equivalent of the triflyl radical CF 3 SO 2 C. This latter species would readily fall apart to give SO 2 and CF 3 C (Scheme 5). A similar transfer of an electron from dihydropyridine to triflic anhydride might thus lead to a pyridinium radical 11$12 and CF 3 C. These pyridinium radicals could possibly expel SO 2 to give the adduct 13, which after an intramolecular nucleophilic addition of the trimethylsilyl ester to the iminium group followed by a CF 3 SO 3 À -induced cleavage of the activated O À SiMe 3 bond in 14 would give lactone 10.…”

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confidence: 89%

Overall “Pseudocationic” Trifluoromethylation of Dihydropyridines with Triflic Anhydride

et al. 2008

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Dihydropyridines of type 2 substituted at the C4-position by a carboxylic acid are valuable intermediates for the synthesis of new heterocyclic compounds, including tetrahydropyridinefused d-lactones 3, polysubstituted tetrahydropyridines 4, and piperidine-fused d-lactones 5 (Scheme 1).[1]The starting materials for all those transformations were differently substituted pyridines, which underwent stepwise nucleophilic addition reactions with ketene acetals 1 upon activation by methyl chloroformate. The ring-closure reaction, leading from 2 to 3, is stereospecific: only the transdiaxial-oriented functionalized lactones are formed. These transformations are part of a special class of reactions of dihydropyridines: nonbiomimetic oxidations, which do not lead, as one would expect, to pyridinium salts.[2] Indeed, the electrophiles preferentially react with one of the double bonds of the ene-carbamates 2 than with the proton at C4.The activation of the pyridinium nucleus towards carbon nucleophiles is not limited to alkyl chloroformates or acid chlorides, since several research groups have also used triflic anhydride for that purpose; in addition to the higher stability of the intermediate pyridinium salts and the general higher yields of the addition products, the absence of rotamers at room temperature is also beneficial.[3] For the purpose of comparing the two activation procedures, with methyl chloroformate or triflic anhydride, we synthesized a series of dihydropyridines subsituted by a triflyl group on the nitrogen atom. This led us to the discovery of a new, unexpected transformation of these dihydropyridines.Thus, the reaction of pyridine with ketene acetals 1 a,b (1 equiv) and then with triflic anhydride (1 equiv) at À30 8C led, as expected, after warming the mixture to room temperature and stirring for 17 h, to the same type of acid-substituted dihydropyridines 7 a,b in high yield (97 %, Scheme 2). Although the reaction of these dihydropyridines with either silica gel or an anhydrous solution of HCl in diethyl ether did not lead to the expected lactones 8 a,b, they did react with I 2 and CuBr 2 to give, as for 2, the corresponding halolactones 9 (Scheme 3). [1,4] However, further studies allowed us to discover a new transformation of these dihydropyridines. Indeed, it appeared that the yield of the dihydropyridines 7 a,b was dependent both on the reaction conditions (order of addition, time of reaction) and on the amount of triflic anhydride used with respect to the starting pyridine: no such an influence was observed when methyl chloroformate was used as the activating agent. The use of an excess of triflic anhydride, however, led to the yield of the dihydropyridines decreasing as a function of time. Surprisingly, according to TLC analysis, Scheme 1. Transformations of dihydropyridines.Scheme 2. Preparation of 7.Scheme 3. Formation of lactone 9.

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“…2 The nucleofugacity of the triflyloxyl group would make this derivative a versatile intermediate from which a particular substituent could be introduced at such position by an S N reaction. 3 Thus, treatment of 10-hydroxycamphor (8a) with triflic anhydride (in the absence of base) gave place to 10-triflyloxycamphor (8b). This derivative proved to be a versatile intermediate for the preparation of other 10-substituted camphors, such as amino or amido derivatives (Scheme 2).…”

Section: Introductionmentioning

confidence: 99%

Unexpected reactivity of 10-hydroxycamphor under triflic anhydride treatment. Formation of a C2-pseudosymmetric camphor-derived sulfite

Martı́nez¹,

Vilar²,

Fraile³

et al. 2009

Arkivoc

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Treatment of enantiopure 10-hydroxycamphor with triflic anhydride and triethylamine yields enantiopure bis(10-camphoryl) sulfite, a novel interesting camphor-based C 2 -pseudosymmetric chiral sulfite with a prochiral sulfonyl group. The process takes place by initial formation of 10-camphoryl triflinate, which undergoes an unexpected nucleophilic substitution with displacement of trifluoromethyl anion (attack of a second equivalent of 10-hydroxycamphor on the sulfur atom). The mentioned pseudosymmetric sulfite has also been obtained by standard reaction of 10-hydroxycamphor with thionyl chloride.

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Chemical Transformations Induced by Triflic Anhydride

Cited by 224 publications

References 253 publications

Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Overall “Pseudocationic” Trifluoromethylation of Dihydropyridines with Triflic Anhydride

Unexpected reactivity of 10-hydroxycamphor under triflic anhydride treatment. Formation of a C2-pseudosymmetric camphor-derived sulfite

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Chemical Transformations Induced by Triflic Anhydride

Cited by 224 publications

References 253 publications

Tf2O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Tf2O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Overall “Pseudocationic” Trifluoromethylation of Dihydropyridines with Triflic Anhydride

Unexpected reactivity of 10-hydroxycamphor under triflic anhydride treatment. Formation of a C2-pseudosymmetric camphor-derived sulfite

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Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids

Tf₂O-Mediated Direct and Regiospecific para-Acylation of Phenols with Carboxylic Acids