Rearrangement and Fragmentation Reactions in Carbenoid Decomposition of Diazo Hydrocarbons

Friedman, Lester; Shechter, Harold

doi:10.1021/ja01489a063

Cited by 122 publications

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“…Ring contraction [1][2] The 1+2 reaction involves a barrier of 78 kJ/mol and an energy release of 222 kJ/moI at the 6-31G** level ( Table 1). The low barrier and the large exothermicity are in agreement with the experimental observations relating to the ease of the isomerization.…”

mentioning

confidence: 99%

Mechanisms of ring contraction, C—H insertion and 1,2‐hydrogen migration of cyclobutylidene

Wang

Deng

1990

Chin. J. Chem.

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Isomerizations of cyclobutylidene 1 to methylenecyclopropane 2, cyclobutene 3 and bicyclobutane 4 have been studied using ab initio method. Equilibrium and transition structures are fully optimized with 3–21G basis set. The reaction barriers are 78, 75 and 110 kJ/mol at 6–31 G**, respectively, 1→2 occurs via the outward disrotation of two end C‐C bonds, 1→3 via the attack of an exo hydrogen to the carbene p AO before the transition state, and 1→4 is unable to compete with 1→2 and 1→3 for its higher barrier.

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mentioning

confidence: 99%

Mechanisms of ring contraction, C—H insertion and 1,2‐hydrogen migration of cyclobutylidene

Wang

Deng

1990

Chin. J. Chem.

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“…If cycloreversion proceeds via such an intermediate (see eq. [5]), then one would expect to observe scrambling of deuterium between positions 3 and 4 of the cyclobutenyl ring, since carbenes of this type are known to undergo ring expansion to the corresponding cyclobutene in addition to fragmentation to alkene and alkyne (49)(50)(51). Examination of the 'H NMR spectrum of an irradiated 0.02 M solution of 2c-d, after ca.…”

Section: Discussionmentioning

confidence: 99%

Cyclobutene photochemistry. Substituent effects on the photochemistry of 1-phenylcyclobutene

Leigh¹,

Postigo²

1995

Can. J. Chem.

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The photochemistry and photophysics of I-phenylcyclobutene and five aryl-substituted derivatives have been studied in various solvents at room temperature. All six compounds fluoresce with quantum yields in the 0.2-0.3 range in cyclohexane and acetonitrile solution. I-Phenylcyclobutene undergoes [2+2]-cycloreversion ( 4 = 0.09) to yield phenylacetylene upon photolysis in either hydrocarbon or acetonitrile solution, and undergoes (Markovnikov) solvent addition upon irradiation in methanol solution ( 4 = 0.08) in addition to cycloreversion. Triplet sensitization and quenching experiments indicate that cycloreversion and methanol addition are both excited singlet state processes. None of the six compounds studied undergo ring opening to the corresponding 2-aryl-1.3-butadiene in detectable yield. Quantum yields for cycloreversion in cyclohexane, acetonitrile, and methanol solution and methanol addition have been determined for the six compounds, along with excited singlet state lifetimes. The quantum yields and rate constants for cycloreversion and methanol addition are both enhanced by substitution with electron-donating groups. ' The variation in the rate constant for [2+2]-cycloreversion with substituent indicates that there is substantial dipolar character developed in the cyclobutenyl a-bond framework during the reaction, in almost exact correspondence with that developed in the .rr system during photoprotonation. No deuterium scrambling is observed in I-phenylcyclobutene-2,4,4-4 after photolysis in pentane solution to ca. 80% conversion, indicating that skeletal rearrangements leading to cyclopropyl carbenes do not occur in the direct photolysis of arylcyclobutene derivatives. A pericyclic mechanism for the photocycloreversion reaction is suggested. Triplet-triplet absorption spectra and triplet lifetimes of I-phenyl-, 1-(porn-methylpheny1)-, and I-fj1arc2-trifluoromethyIphenyl)cyclobutene in hydrocarbon solution are also reported.Key words: photochemistry, cyclobutene, fluorescence, [2+2]-cycloreversion, substituent effects, nanosecond laser flash photolysis, lifetime, triplet state, styrene, photoaddition Resume : On a CtudiC, dans differents solvants et 6 diffkrentes temperatures, la photochimie et la photophysique du I-phenylcyclobutkne et de cinq derives aryles substitues. Tous ces six composes entrent en fluorescence avec des rende~nents quantiques de l'ordre de 0.2 6 0,3 en solution dans le cyclohexane et dans I'acCtonitrile. Le I -phCnylcyclobutkne subit une cycloCIimination [2+2] ( 4 = 0,09) pour conduire au phCnylacCtylkne par photolyse en solution dans un hydrocarbure ou dans I'ac6tonitrile. avec en plus une addition de solvant (de type Markovnikov) par irradiation dans une solution de methanol ( 4 = 0,08). Les experiences de sensibilisation du triplet et de dksactivation indiquent que la cycloClimination et I'addition de methanol sont toutes deux des Ctats singulets excites. Aucun des six composCs CtudiCs ne conduit par ouverture du cycle au 2-aryl-1,3-butadikne en quantite dCcelable. On ...

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“…48,49 Tang and coworkers have reported a transition-metal-mediated variant in which significant improvements in the yields and selectivities were observed. 50 Several transition metal complexes were evaluated, from which AgOTf emerged as the catalyst of choice (Scheme 8.20).…”

Section: Ring Expansion Reactionsmentioning

confidence: 99%

Silver Carbenoids

Lovely¹

2010

Silver in Organic Chemistry

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Rearrangement and Fragmentation Reactions in Carbenoid Decomposition of Diazo Hydrocarbons

Cited by 122 publications

References 0 publications

Mechanisms of ring contraction, C—H insertion and 1,2‐hydrogen migration of cyclobutylidene

Mechanisms of ring contraction, C—H insertion and 1,2‐hydrogen migration of cyclobutylidene

Cyclobutene photochemistry. Substituent effects on the photochemistry of 1-phenylcyclobutene

Silver Carbenoids

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