Cyclopropylcarbinyl Radical Research Articles

Ethoxycarbonyl acceleration of cyclopropylcarbinyl radical ring opening

Rate constants for ring opening of the [ trans-(2-ethoxycarbonyl)cyclopropyl]methyl radical were determined by competition kinetics employing benzeneselenol trapping.

Cytochrome P450 hydroxylation of hydrocarbons: variation in the rate of oxygen rebound using cyclopropyl radical clocks including two new ultrafast probes.

The oxidation of eight methyl-substituted and three alkyl-substituted cyclopropanes by rat liver microsomal cytochrome P450 and pure reconstituted rabbit P450 2B4 was studied. Alkane hydroxylation catalyzed by P450 is generally believed to proceed by hydrogen abstraction followed by reaction of the carbon-centered radical with an iron-bound hydroxyl radical, a process called oxygen rebound. Hydrogen abstraction from methylcyclopropanes generates cyclopropylcarbinyl radicals whose solution rate constants for ring opening are known [Bowry, V.W., et al. (1991) J. Am. Chem. Soc. 113, 5687-5698]. Rearranged products were only observed with the five substrates which, upon hydrogen abstraction, would generate a cyclopropylcarbinyl radical that undergoes ring opening with a rate constant > or = 2.0 x 10(9) s-1 in solution. Values of the rate constants for oxygen rebound (kOH) were calculated by determining the ratio of unrearranged products (cyclopropylmethanols) to rearranged products (alkenols). For each substrate this ratio was generally about the same for the oxidations catalyzed by microsomal P450 and by P450 2B4. It is concluded that all of the substrates are oxidized via an intermediate cyclopropylcarbinyl radical. Two ultrafast probes, trans-1-methyl-2-phenylcyclopropane and 1,1-diphenyl-2-methylcyclopropane, gave alcohol product ratios which yielded unreasonably high values for kOH, viz., ca. 1.5 x 10(12) and ca. 7 x 10(12) s-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

ChemInform Abstract: Picosecond Radical Kinetics. Ring Openings of Phenyl Substituted Cyclopropylcarbinyl Radicals.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Picosecond radical kinetics. Ring openings of phenyl-substituted cyclopropylcarbinyl radicals

Rate constants for ring openings of the trans-(2-phenylcyclopropyl)carbinyl radical (1a), the cis-(2-phenylcyclopropyl)carbinyl radical (1b), and the (2,2-diphenylcyclopropyl)carbinyl radical (1c) were studied by competition kinetics using PTOC esters as radical precursors and hydrogen atom transfer trapping from benzeneselenol as the basis reaction. Radical 1a was studied in two solvents, toluene and THF; the experimental Arrhenius function for ring opening of 1a was log (κ r .s)=13.9-3.3/2.3RT (R in kcal/mol)

Picosecond radical kinetics. Rate constants for reaction of benzeneselenol with primary alkyl radicals and calibration of the 6-cyano-5-hexenyl radical cyclization

The cyclopropylcarbinyl radical ring opening was used as a radical clock to determine rate constants for benzeneselenol trapping in THF and in toluene. Hydrogen atom transfer trapping from PhSeH appeared to be partially diffusion controlled. An operational Arrhenius function for trapping in THF is log (k T .M s)=11.03-2.27/2.3RT. The recommended function for PhScH trapping in other low-viscosity organic solvents is log (k T .M s)=10.87-2.10/2.3RT. The rate constant for trapping at 25 o C is 2.1×10 9 M -1 s -1

ChemInform Abstract: Use of Radical Ring‐Opening for Introduction of Alkyl and Substituted Alkyl Groups with Stereochemical Control: A Synthetic Application of Cyclopropylcarbinyl Radicals.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Calibration of a new horologery of fast radical clocks. Ring-opening rates for ring- and .alpha.-alkyl-substituted cyclopropylcarbinyl radicals and for the bicyclo[2.1.0]pent-2-yl radical

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCalibration of a new horologery of fast radical clocks. Ring-opening rates for ring- and .alpha.-alkyl-substituted cyclopropylcarbinyl radicals and for the bicyclo[2.1.0]pent-2-yl radicalVincent W. Bowry, Janusz Lusztyk, and K. U. IngoldCite this: J. Am. Chem. Soc. 1991, 113, 15, 5687–5698Publication Date (Print):July 1, 1991Publication History Published online1 May 2002Published inissue 1 July 1991https://doi.org/10.1021/ja00015a024RIGHTS & PERMISSIONSArticle Views1256Altmetric-Citations176LEARN 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 (1 MB) Get e-Alerts Get e-Alerts

Use of radical ring opening for introduction of alkyl and substituted alkyl groups with stereochemical control: a synthetic application of cyclopropylcarbinyl radicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUse of radical ring opening for introduction of alkyl and substituted alkyl groups with stereochemical control: a synthetic application of cyclopropylcarbinyl radicalsDerrick L. J. Clive and Sylvain DaigneaultCite this: J. Org. Chem. 1991, 56, 12, 3801–3814Publication Date (Print):June 1, 1991Publication History Published online1 May 2002Published inissue 1 June 1991https://doi.org/10.1021/jo00012a009RIGHTS & PERMISSIONSArticle Views786Altmetric-Citations64LEARN 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 (2 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The photochemical generation of .alpha.-sulfur-substituted cyclopropylcarbinyl radicals and their utilization as a mechanistic probe for electron transfer in the peroxide-sulfide reaction

We present the results of our products studies on the reaction of tetramethyl-1,2-dioxetane and of benzoyl peroxide with cyclopropylcarbinyl-substituted sulfides, in which we demonstrate that non cyclopropylcarbinyl ring-opened products were formed, although independently generated, α-sulfur-substituted cyclopropylcarbinyl radicals rearrange efficiently. The mechanistic implications of these findings with respect to the peroxide-sulfide reaction will be discussed

Ring opening and hydrogen-atom transfer trapping of the bicyclo[2.1.0]pent-2-yl radical

Relative rate constants (k r /k H ) for ring opening of the bicyclo [2.1.0] pent-2-yl radical (1) to the cyclopent-3-enyl radical and trapping of radical 1 with t-BuSH, PhSH, and PhSeH in solvent THF were measured at temperatures between −78 and 50 o C. The hydrogen atom donors reacted more rapidly with radical 1 than with the cyclopropylcarbinyl radical. Rate constants for ring opening of 1 (k r ) could be obtained by estimating the values of k H via Marcus theory

Rearrangement of rigid cyclopropylcarbinyl radicals: investigation of a reporter system for the detection of very short-lived radicals

Rearrangement of rigid cyclopropylcarbinyl radicals: investigation of a reporter system for the detection of very short-lived radicals

Formation of 2,3‐Dihydrothiophene‐3‐carboxylates from 2(5H)‐Thiophenones via Sequential Cyclization and Ring‐Opening Reactions of 3‐Thiahexa‐1,5‐dienyl Radicals. Preliminary Communication

AbstractMethyl 4‐mercapto‐2‐alkenoates 1, obtained by irradiation of 2(5H)‐thiophenones 2 in MeOH, undergo light‐induced S–H bond homolysis to give thio radicals 3 which can be trapped with 2‐butyne to afford 3‐thiahexa‐1,5‐dienyl radicals 12. Intermediates 12 undergo selective 1,5‐ring closure to allylcarbinyl radicals 18, which cyclize to cyclopropylcarbinyl radicals 19. A novel rearrangement of 19 to 23, the direct precursors of title compounds 15 and 17, occurs via two additional ring‐opening and one 1,5‐ring‐closure step.

The effects of the cyclopropyl group on a radical center

The cyclopropylcarbinyl radical 1, the methylcyclopropyl radical 2 and the homoallyl radical 3 have been computed by ab initio methods (full geometry optimization and polarized basis set). The smallness of the rotational barrier in 1 relative to the allyl radical is explained by a perturbational molecular orbital (PMO) analysis: it is found that the interaction energy of the mono-occupied p orbital with the ring is the same in both conformers, the difference between them coming essentially from the π CH 2 , and π CH 2 * orbitals. Thus in this case, the rotational barrier is not related to the delocalization energy. This behavior is compared with that of the allyl radical.

EPR spectroscopic study of free-radical addition of mercaptans and polyhalomethanes to substituted alkenylcyclopropanes by spin trapping

1. Using nitrosodurene as a spin trap, the addition of CCl3 and PhS radicals to substituted alkenylcyclopropanes was studied by EPR. The formation of spin adducts of cyclopropylcarbinyl and allylcarbinyl radicals with nitrosodurene was established. 2. The rate constant of the isomerization of cyclopropylcarbinyl to allylcarbinyl radicals was determined and it was shown that this rearrangement is quite rapid (isomerization constant 106–107 sec−1).

On the question of free radical intermediacy in cycloaddition reactions of diazocarbonyl compounds to olefins under copper(II) chelate catalysis

The Copper(II) chelate catalyzed thermal cycloaddition of ethyl diazoacetate, dimethyl diazomalonate, ethyl-2-diazo-3-oxobutyrate, and ethyl diazopyruvate, representatives of diazocarbonyl additions that yield cyclopropanes and dihydrofurans, respectively, to olefins, has been examined in terms of the possible participation of radical species in intermediary stages. To this purpose, the title diazocarbonyl compounds were exposed to 1-methyl-1-cyclopropylethylene and 1,1-dicyclopropylethylene under catalytic conditions. The absence of cyclopropylcarbinyl radical to butenyl radical rearrangement products in cyclopropanations as well as in those reactions that furnish heterocycles suggests that intermediates of free radical nature may not be involved in the cycloaddition process. In turn, the strong electron donor capability of cyclopropyl substituents is interpreted as allusive of a non synchronous 1,3-dipolar cycloaddition of transient metal carbenes to the olefin with possible charge polarization.

Substituent control of cyclopropylcarbinyl radical ring opening reactions

Substituent control of cyclopropylcarbinyl radical ring opening reactions

The regioselective ring-opening of ring-substituted cyclopropylcarbinyl radicals: variation of the substituent

The cis- and trans-2-ethyl- and 2-t-butyl-cyclopropylcarbinyl radicals (A; M = H or Bu3Sn; R = Et or But) were generated by the addition of tributyltin radicals to the appropriate ketone, or abstraction of hydrogen from the appropriate carbinols, and the intermediate radicals and the ultimate products were monitored by e.s.r. spectroscopy [graphic omitted] and by g.l.c. respectively. It is shown that the ethyl and t-butyl substituents exert the same directive effect as the methyl group in that whereas the cis-reactants undergo ring opening to give predominantly the secondary alkyl radicals (B) the trans-reactants give the thermodynamically less stable primary alkyl radicals (C).

An ab initio calculation of the cyclopropylcarbinyl radical

Ab initio calculations at minimal (STO-3G) and extended (4-31G) basis levels have been carried out for the cyclopropylcarbinyl radical using the unrestricted Hartree-Fock procedure. It is found that the ordering of the long-range proton isotropic hyperfine coupling constants are opposite to the results obtained from semi-empirical INDO calculations. The coupling constants for the extended basis set are a exo = −1.71 G, a endo = −4.25 G, a β= 11.41 G, a α1 = −66.01 G and a α2 = −64.73 G.

ChemInform Abstract: SPECIFIC β‐SCISSION OF 3β,5‐CYCLOCHOLESTAN‐6‐YL RADICAL

AbstractAusgehend vom Cholestadien (I) wird über die Stufen (II), (III) und (IVa) das Cyclocholestan (IVb) dargestellt; bei der Einwirkung von Triphenylstannan (V) auf (IVb) wird zunächst das Radikal (VI) erzeugt, das eine spezifische β‐Spaltung der 4,5‐Bindung unter Bildung des thermodynamisch weniger stabilen Radikals (VII) eingeht.

ChemInform Abstract: HOMOALLYLIC REARRANGEMENTS OF 4‐SPIRO(2,4)HEPTYL RADICAL AND 4‐SPIRO(2,5)OCTYL RADICAL

AbstractAus den Ketonen (Ia) und (Ib) entstehen die Azine (IIa) und (IIb), die mit verschiedenen Reduktionsmitteln zu den Azo‐Verbindungem (IIIa) und (IIIb) reduziert werden.