Mechanisms of singlet oxygen reactions.  Intermediates in the reaction of singlet oxygen with dienes

Hasty, Noel M.; Kearns, David R.

doi:10.1021/ja00791a050

Cited by 75 publications

(18 citation statements)

References 8 publications

(8 reference statements)

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“…This dipolar transition state accounts, a t least qualitatively, for the previously observed dependence of rates and product composition on solvent [27]. The interesting finding that a nucleophilic solvent can compete with oxygen for allylic hydrogen is inconsistent with the convcntional fully concerted ene mechanism, but fits the meclianism proposed here /28j.…”

Section: Methodssupporting

confidence: 66%

Reaction of Singlet Oxygen with 2‐Methylnorborn‐2‐ene, 2‐Methylidenenorbornane, and their 7,7‐Dimethyl Derivatives. The transition state geometry for hydroperoxidation

Jefford

Boschung

1974

Helvetica Chimica Acta

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The dye-sensitized photo-oxygenation of 2-meth ylnorborn-2-ene (3), 2-niethylidenenorbornane (4) and their 7,7-dimethyl derivatives (5 and 6) has been studied. In all cases allylically rearranged hydroperaxides WCTe formed, cxcept that 4 also gave a little norbornanone (presumably from the dioxetane) and 5 gave some endo-3,7,7-trinicthylnorbornan-2-one as a secondary photoproduct. It was found that the exolendo attack ratios by singlet oxygen on 3 and 5 are 66 and 0.19. By exploiting the C (3) monodeuteriated derivativcs, 4 and 6 showed ratios of 28 and 0.67.Rates of reactivity of the olefins 3 and 4 were compared t o methylidenecyclopentane, I-methycyclopentene and 1-rnethylcyclohexene as monocyclic standards. Additionally, comparative rates between the 7,7-dimethyl olefins and their parents were measured. When further comparison was made of the rate ratios partitioned for exo and endo attack, it was seen that oxygen expericnced a 500-to 1000-fold rate retardation on approach to the endcs side of 3 compared to that for its monocyclic analogue. Exo rates between the parent norbornene 3 and its 7,7-dimethyl derivative 5 showed a 250-fold decrease. Although four times snialler than the difference reported for epoxidation, the evidence clearly pointed t o a one-step cyclic process as the rate determining step for photo-oxygenation. The steric cvidence, taken with the low valucs found for the intermolecular isotope effects of 1.14 & 0.01 and 1.02 & 0.01 observed for exo and endo-3-deutcrio-2-methylidenenorbornanes, permits the deduction that the transition state is largely dipolar. In the early stagcs of the addition bonding between one end of the oxygen molecule and the terminal vinyl carbon is advanced. At the same time positive charge is dispersed by hyperconjugation between the central carbon atom and the allylic carbon-hydrogen bond. A t a latcr stage the anionic oxygen atom abstracts the loosened allylic hydrogen atom to create the hydroperoxide. No evidence for the formation of a discrete perepoxide intermediate was obtained

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Section: Methodssupporting

confidence: 66%

Reaction of Singlet Oxygen with 2‐Methylnorborn‐2‐ene, 2‐Methylidenenorbornane, and their 7,7‐Dimethyl Derivatives. The transition state geometry for hydroperoxidation

Jefford

Boschung

1974

Helvetica Chimica Acta

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“…We have surveyed a number of cyanines (Table 3) to compare their overall *Kearns (1969) has correlated the efficiency of the "ene" reaction with the oxidation potential of the substrate. Recent evidence indicates that 1,2 additions may proceed through formation of peroxirane intermediates (Hasty and Kearns, 1973;Schaap and Falen, 1973), which should have polar contributions to the transition state.…”

Section: Resultsmentioning

confidence: 99%

Direct and Sensitized Photooxidation of Cyanine Dyes

Byers

Gross

Henrichs

1976

Photochem & Photobiology

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Direct photooxidation of cyanine dyes was found to be markedly enhanced by formation of hypsochromically shifted (H) aggregates. Singlet oxygen was found to attack many cyanines possessing low oxidation potentials with rate constants in excess of lo8 / mol-I s-I. Singlet oxygen attack on 3,3'-diethyl-8,1O-dimethylthiacarbocyanine yields carbonyl products consistent with 1,2 addition to the 2,8 bond of the methine chain.

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“…neo-abietic acid (Schuller and Lawrence, 1967). An ene reaction takes place which causes the displacement of the double bond and the formation of a conjugated system, followed by a dienophilic But Hasty and Kearns (1973), in the case of 2,5-dimethyl-2,4-hexadiene suggest the occurrence of a l+cycloaddition besides a competition between an addition of oxygen to the latter:…”

mentioning

confidence: 99%

Singlet Oxygen Reactions With 2,7‐dimethyl‐2,6‐octadiene

Taniélian

Chaineaux

1978

Photochem & Photobiology

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Abstract— Results concerning Rose Bengal sensitized photoxidation of 2,7‐dimethyl‐2,6‐octadiene (A) are discussed. This diolefin may be considered as a model molecule of polyisoprene of polymerization number two with 1,4‐4,1 addition mode. All the mono‐ and dihydroperoxides apt to occur are actually obtained. One of the occurring hydroperoxides, 2,7‐dimethyl‐dihydroperoxy‐3,5‐octadiene, which has the structure of a conjugated diene, does not lead to an endoperoxide. This is contrary to Kaplan and Kelleher's hypothesis. On the other hand, no trihydroperoxide forms as a result of further addition of singlet oxygen (1O2). A complete kinetic study has allowed us to determine the rate constants of all the reactions which take place. The reactivity of (A) is twice that of 2‐methyl‐2‐pentene and the addition of 1O2 to one of the double bonds of (A) induces deactivation of the remaining double bond.

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Mechanisms of singlet oxygen reactions. Intermediates in the reaction of singlet oxygen with dienes

Cited by 75 publications

References 8 publications

Reaction of Singlet Oxygen with 2‐Methylnorborn‐2‐ene, 2‐Methylidenenorbornane, and their 7,7‐Dimethyl Derivatives. The transition state geometry for hydroperoxidation

Reaction of Singlet Oxygen with 2‐Methylnorborn‐2‐ene, 2‐Methylidenenorbornane, and their 7,7‐Dimethyl Derivatives. The transition state geometry for hydroperoxidation

Direct and Sensitized Photooxidation of Cyanine Dyes

Singlet Oxygen Reactions With 2,7‐dimethyl‐2,6‐octadiene

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