164171-91-9Relevant articles and documents
Novel Selective Approach to Terminally Substituted [n]Dendralenes
Polák, Peter,Tobrman, Tomá?
supporting information, p. 957 - 968 (2018/12/11)
Dendralenes are simple alkenes with cross-conjugated double bonds that are frequently synthesized due to being potentially valuable building blocks for the synthesis of more complex structures. The synthetic approaches to dendralenes are based on the cross-coupling reactions of electrophilic and nucleophilic synthons derived from geminally substituted ethylene. Our novel methodology for the synthesis of only terminally substituted [3]- and [4]dendralenes, as well as 2,3-disubstituted buta-1,3-dienes, involves the preparation of 1,2-disubstituted cyclobutenes from readily available 2-bromocyclobutanone and the subsequent thermal ring-opening reactions.
Cyclobutene photochemistry. Substituent effects on the photochemistry of 1-phenylcyclobutene
Leigh, William J.,Postigo, J. Alberto
, p. 191 - 203 (2007/10/02)
The photochemistry and photophysic of 1-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. 1-Phenylcyclobutene undergoes -cycloreversion (γ = 0.09) to yield phenylacetylene upon photolysis in either hydrocarbon or acetonitrile solution, and undergoes (Markovnikov) solvent addition upon irradiation in methanol solution (γ = 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 cycloreversion with substituent indicates that there is substantial dipolar character developed in the cyclobutenyl ?-bond framework during the reaction, in almost exact correspondence with that developed in the ? system during photoprotonation.No deuterium scrambling is observed in 1-phenylcyclobutene-2,4,4-d3 after photolysis in pentane solution to ca. 80percent conversion, indicating that sleletal 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 1-phenyl-, 1-(para-methylphenyl)-, and 1-(para-trifluoromethylphenyl)cyclobutene in hydrocarbon solution are also reported. Key words: photochemistry, cyclobutene, fluorescence, -cycloreversion, substituent effects, nanosecond laser flash photolysis, lifetime, triplet state, styrene, photoaddition
