Cation Radical Cycloadditions Research Articles

New Polymer Structures and Polymerization Mechanisms Based upon Cation Radical Cycloadditions

New Polymer Structures and Polymerization Mechanisms Based upon Cation Radical Cycloadditions

The Cation Radical Chain Cycloaddition Polymerization ofN,3-Bis(trans-1-propenyl)carbazole: The Critical Importance of Intramolecular Hole Transfer in Cation Radical Cycloaddition Polymerization

The synthesis and polymerization of N,3-[bis(trans-1-2)]carbazole (1) is reported. Using either the stable cation radical salt tris(4-2)aminium hexachloroantimonate (2 +.) or anodic oxidation to initiate the reaction, novel cycloaddition polymers are obtained in which the intermonomer linkages are of the cyclobutane, and to some extent of the Diels−Alder, type. A novel cation radical chain mechanism is proposed for the reaction, and extensive support for this mechanism is presented. The greatly enhanced reactivity of difunctional, as opposed to monofunctional, substrates in cation radical cycloadditions is dramatically highlighted by a comparison of the cycloaddition reactivity (rapid polymerization) of 1 versus N-propenylcarbazole (inefficient cyclodimerization) under electrochemical oxidation conditions. The sharply enhanced reactivity of 1 is attributed to the availability of intramolecular hole transfer in the bifunctional but not the monofunctional case.

Approaching a possible stepwise/concerted mechanistic crossover point in the cation radical cycloadditions of cis- and trans-anethole

The Diels–Alder cycloadditions of the cis- and trans-anethole cation radicals to cyclopenta-1,3-diene have carefully been examined and are found to produce sharply different stereochemical results. The cis-anethole cation radical adds via a distinctly stepwise mechanism, yielding comparable amounts of all four diastereoisomeric Diels–Alder adducts. In contrast, the trans-anethole cation radical yields only trans adducts, with the endo isomer predominating. None of the cis adducts could be detected, and the percentage of cis adducts formed, if any, is significantly less than 0.1%. This result stands in contrast to the additions of aryl cis- and trans-propenyl ethers to the same diene, in which both geometric alkene isomers yield all four adducts in comparable amounts. Consequently, if trans-anethole also reacts by a stepwise mechanism, the rate of cyclization in the intermediate distonic cation radical must be of the order of 1000 times the rate of bond rotation. Alternatively, although it is less likely, the trans cation radical could react via a concerted reaction path.

The mechanism of the prototype cation radical cycloaddition reaction: the cyclodimerization of N-vinylcarbazole

The mechanism of the first cation radical cycloaddition reaction to be discovered, the cyclodimerization of N-vinylcarbazole, has now been studied by means of a stereochemical criterion. The cyclodimerization of N-(cis-2-deuteriovinyl)carbazole is observed to be non-stereospecific, yielding a cyclodimer in which approximately 80% of the deuterium atoms are cis to the carbazolyl group and 20% are trans to the carbazolyl group. This result stands in contrast to the stereospecific cyclodimerization of trans- and cis-anethole and other stereospecific cation radical cyclobutanation reactions which have been studied more recently. The cyclodimerization of N-vinylcarbazole must therefore occur via a stepwise path, involving an intermediate distonic cation radical, as originally proposed by the Ledwith group. Further, the gauche conformation of the distonic cation radical is implied to be preferred over the anti form.

Cation radical cycloaddition polymerization: Diels–Alder copolymerization

The Diels–Alder cycloaddition copolymerization of a bis(diene) with ionizable bis(dienophiles) via a cation radical mechanism has been accomplished using tris(4-bromophenyl)aminium hexachloroantimonate as a catalyst in dichloromethane solvent. The reactions occur at 0°C and yield Diels–Alder polymers of MW up to ca. 10,000 and a polydispersity index ca. 2. © 1998 John Wiley & Sons, Ltd.

The reaction of allylic esters of dithiocarboxylic acids with tetracyanoethylene affording 3,3,4,4-tetracyano-6,8-dithiabicyclo[3.2.1]octanes

A range of substituted 3,3,4,4-tetracyano-6,8-dithiabicyclo[3.2.1]octanes, viz. compounds 5dg, 5j–m, and 5o–u, have been synthesized from the corresponding allyl dithiocarboxylates by a cation radical cycloaddition reaction, using tetracyanoethylene 2 in acetonitrile. The reaction scope has been studied and the mechanism proposed on the basis of the dithioester's chemical behaviour in respect to oxidizing agents, mass-spectrometry data, the substituent effect analysis as well as by quantum chemical calculations by the MINDO/3 method in UHF approach.

1,3-Diketonatoboron difluoride sensitized cation radical reactions

Dibenzoylmethanatoboron difluoride (DBMBF2) and allied BF2 complexes interact from their singlet excited state with trans-anethole (t-A), quadricyclene (QC), and norbornadiene (NBD) by electron transfer to generate the corresponding cation radicals, which undergo the reported reactions. By sensitization, t-A undergoes dimerization to form the anti head-to-head and syn head-to-head dimers with retention of stereochemistry. The formation is reversible under sensitization conditions, leading to accumulation of the more stable anti isomer. However, irradiation of the absorption band of the DBMBF2 – t-A ground state complex did not lead to dimerization of t-A. By DBMBF2 sensitization, QC is cleanly converted to NBD while NBD is not affected. The calculation shows QC+• possesses higher energy than NBD+• by 7.5 kcal/mol, hence an irreversible rearrangement. Other sensitizers (e.g., cyanoaromatics and tetrachlorobenzoquinone) also promote these cation radical reactions but not as cleanly as DBMBF2. Key words: photosensitization by boron complexes, cation radical rearrangement, cation radical cycloaddition, electron transfer sensitization, photoreaction of ground state complexes.

ChemInform Abstract: Cation Radical Cycloadditions and Related Sigmatropic Reactions

ChemInform Abstract: Cation Radical Cycloadditions and Related Sigmatropic Reactions

Cation radical cycloadditions and related sigmatropic reactions

Cation radical cycloadditions and related sigmatropic reactions

Theoretical study of the symmetry forbidden concerted ethene-ethene cation radical cycloaddition reaction

To examine the reduced symmetry restrictions on the kinetically facile cycloaddition of ethene-ethene cation radical, portions of relevant quasiadiabatic potential energy surfaces are explicitly constructed through ab initio MO calculations at the Hartree-Fock level. The 2 s + 1 s mode is chosen as the reaction coordinate. Through the analysis of spin transfer during the course of the transition, the most stable adduct is found to possess an open structure (the 1,4-butane cation radical) The chain mechanism as proposed by Bauld is confirmed if the cycloaddition is allowed to take a nonconcerted path. The limitation of the quasiadiabatic potential surface approach is noted. The kinetic effect of a three-electron bond is examined.

Theoretical reaction paths for cation radical cycloadditions : The [3+2] or role-reversed cation radical diels-alder

An extended basis set ab initio reaction path calculation for the prototype role-reversed cation radical Diels-Alder reveals that even this symmetry-forbidden cyclization mode proceeds without activation, at least in the gas phase. An intermediate, termed a long-bond complex, is encountered on the path, but the energy minimum is so shallow that the reaction is considered likely to be concerted when entropy effects are considered. The calculation further reveals that the factor which importantly distinguishes the role-reversed cycloaddition mode from the allowed cycloaddition mode, namely, the presence of charge predominantly on the diene moiety as contrasted to the dienophilic moiety, is maintained well along the reaction path and even in the long-bond intermediate. Competition between the role-reversed Diels-Alder and a competing [2+1] cyclobutane cycloaddition is envisioned.

Selective cyclobutane adduct formation in competition with Diels-Alder addition in cation radical cycloadditions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelective cyclobutane adduct formation in competition with Diels-Alder addition in cation radical cycloadditionsRaul A. Pabon, Dennis J. Bellville, and Nathan L. BauldCite this: J. Am. Chem. Soc. 1984, 106, 9, 2730–2731Publication Date (Print):May 1, 1984Publication History Published online1 May 2002Published inissue 1 May 1984https://doi.org/10.1021/ja00321a059RIGHTS & PERMISSIONSArticle Views305Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (296 KB) Get e-Alerts Get e-Alerts

Cation-Radical Cycloaddition and Polymerization Reactions of N-Vinylcarbazole with Electrophilic Ethylenes

Abstract The uncatalyzed reactions of N-vinylcarbazole with electrophilic olefins have been studied. The products included both small molecules and polymers. N-Vinylcarbazole reacted with tricarbomethoxyethylene in inert solvents such as benzene at 110°C to form trimethyl 1-carbazol-9-ylbut-1-ene-3,4,4-tricarboxylate. Donor solvents such as acetone or acetonitrile gave trimethyl-1-carbazol-9-ylcyclobutane-2,2,3-tricarboxylate. A variety of additives in the inert solvents also diverted the product from the 3,4,4-tricarboxylate to the 2,2,3-tricarboxylate. These included oxygen, several silver salts, metallic mercury, diphenylpicrylhydrazyl, and tributyltinhydride. Polymers also formed in low yields in many of these reactions. Either homo-polyvinylcarbazole or the alternating copolymer of N-vinylcarbazole with tricarbomethoxyethylene formed, depending on the solvent. Pyridine prevented the formation of the former, and tert-butylhydroquinone the latter; thus their formation is ascribed to cationic and free r...