<i>Ab Initio </i>Theoretical Studies on the Ring-Opening Modes of the Oxiranyl-, Aziridinyl-, Oxaziridinyl-, and Thiaranylmethyl Radical Systems

Pasto, Daniel J.

doi:10.1021/jo9505942

Cited by 26 publications

(26 citation statements)

References 9 publications

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“…While there is not much precedent for this mode of oxirane ring opening, it is rather similar to the welldocumented easy opening of oxiranylmethyl radicals. 14 Initial activation of an oxirane ring C-H bond is nearly as easy as methyl C-H activation. However, the subsequent C-O cleavage step has a prohibitively high barrier, making this a non-productive path.…”

Section: Dft Results For Oxirane Openingmentioning

confidence: 99%

C–H and C–O bond activation with a rhodium(i) β-diiminate complex

2014

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Complex LRh(COE) [L = (2,6-Me2C6H3NCMe)2CH; COE = cyclooctene] reacts with oxirane, methyloxirane and 2,2-dimethyloxirane to eventually produce LRh(COE)(CO) and alkane (methane, ethane, propane). This reaction and other aspects of the reactivity of the "LRh" fragment (hydrogenation of olefins and benzene) have been studied by density functional theory. The results indicate that for 2,2-dimethyloxirane (and probably also for methyloxirane) the reaction starts with C-H activation of a methyl group, followed by ring opening and decarbonylation. For the parent oxirane, where this path is not available, the reaction starts with C-O activation to form a 2-rhodaoxetane, which then undergoes β-elimination. More generally, easy C-H activation, which appears to be a recurring theme in this Rh chemistry, is due to a close energy matching between corresponding Rh(i) and Rh(iii) complexes. For the analogous Ir complexes, preference for higher oxidation states is larger, leading to significantly higher barriers for e.g. hydrogenation.

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Section: Dft Results For Oxirane Openingmentioning

confidence: 99%

C–H and C–O bond activation with a rhodium(i) β-diiminate complex

2014

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“…The results of a recent calculational study carried out in the author's laboratories using various calculational methods including UHF, UMP2, MCSCF and employing many different split-level basis sets, including diffuse and polarization functions, on the oriranylmethyl-allyloxy-vinyloxymethyl 14 and other similarly related systems, 15 have indicated that geometry optimization calculations carried out at the UHF/6-31G ଙ level of theory followed by a single-point calculation at the QCISD(T)/6-31G…”

Section: Calculational Methodsmentioning

confidence: 99%

Theoretical analysis of the energy barriers for the rotational isomerization of the allyl and the 1-cyano-, 1-hydroxy- and 1-cyano-1-hydroxyallyl radicals

Pasto

1997

J. Phys. Org. Chem.

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An ab initio computational study was carried out on the ground-and transition-state structures for the rotational isomerization of the allyl and the 1-cyano, 1-hydroxy-and 1-cyano-1-hydroxyallyl radical systems in an attempt to gain an understanding of the factors affecting the relative energy barriers for rotational isomerization. The results of ESR rate measurements have indicated that there exists the presence of an 'extra' lowering of the energy barrier for the rotational isomerization of the 1-cyano-1-hydroxylallyl radical relative to the sum of the lowerings of the energy barriers for the rotational isomerization of the 1-cyano-and 1-methoxylallyl radical compared with the energy barrier for the rotational isomerization of the allyl radical. The 'extra' lowering of the energy barrier for the rotational isomerization of the 1-cyano-1-hydroxyallyl radical has been attributed to captodative stabilization of the transition structure for rotational isomerization. Prior calculational studies in the author's and other laboratories have resulted in the suggestion that captodative substitution does not always lead to 'extra' stabilization to a radical center. Recent calculations in the author's laboratories and the results reported in the present paper strongly suggest that ground-state effects can be dominant in determining the rate of a radical-forming reaction. The present paper describes the results of theoretical calculations on the allyl and substituted allyl radical systems that indicate that ground-state effects appear to dominate the relative rates of the rotational isomerization of the substituted allyl radicals.

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“…Indispensable information about the intermediates has been obtained from ab initio molecular calculations 15. 16 It was found that ring opening is exothermic for cleavage of both CO or CC bonds (Scheme ).…”

Section: Epoxide Oxetane and Aziridine Opening Through Generatiomentioning

confidence: 99%

Strained Heterocycles in Radical Chemistry

2003

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Over the last few decades the use of radicals in synthesis has witnessed an explosive growth through introduction of efficient chain and electron-transfer reactions. Strained heterocycles, in particular, have emerged as a highly versatile and readily available class of radical precursors. The generation of carbinyl radicals of heterocycles has resulted in many elegant applications of heteroatom-centered radicals, such as beta fragmentations, cyclizations, and intramolecular hydrogen atom abstractions. Direct electron transfer to strained heterocycles has been realized through the use of arene radical anions. The method combines the virtues of radical and organometallic chemistry to yield useful functionalized organolithium compounds. Epoxides have been opened with high regioselectivity by titanocene(III) reagents in either stoichiometric or catalytic quantities to yield beta-titanoxy radicals. This development has resulted in many new applications in natural product synthesis.

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Ab Initio Theoretical Studies on the Ring-Opening Modes of the Oxiranyl-, Aziridinyl-, Oxaziridinyl-, and Thiaranylmethyl Radical Systems

Cited by 26 publications

References 9 publications

C–H and C–O bond activation with a rhodium(i) β-diiminate complex

C–H and C–O bond activation with a rhodium(i) β-diiminate complex

Theoretical analysis of the energy barriers for the rotational isomerization of the allyl and the 1-cyano-, 1-hydroxy- and 1-cyano-1-hydroxyallyl radicals

Strained Heterocycles in Radical Chemistry

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