Cyclobutene photochemistry. Nonstereospecific photochemical ring opening of simple cyclobutenes

Clark, K. B.; Leigh, William J.

doi:10.1021/ja00254a030

Cited by 33 publications

(40 citation statements)

References 2 publications

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“…Cis-and trans-2-butene and propyne were used for VPC analyses as received from Canada Liquid Air, Inc. 2-Butyne for VPC spiking experiments was part of a calibrated mixture of Cz-C4 alkynes (Scott, Inc.). Cyclobutenes cis-and trans-1 were synthesized as part of our earlier study (1). E and Z-ethylidenecyclohexene (7) were synthesized as a mixture according to the published procedure (25).…”

Section: Methodsmentioning

confidence: 99%

“…stereochemistry of the photochemical ring opening of simple have been reported to do so non-stereos~ecifically ( 5 ) and alkylcyclobutenes (1). Prior to this study, there existed only one Dewar aromatics open adiabatically (6).…”

Section: Introductionmentioning

confidence: 92%

“…Control experiments were carried out to ensure that the relative product yields reported in Tables 2 and 3 correspond to primary photolysis yields, and suffer no distortion due to secondary photolysis of the dienes (1,20). To this end, we have photolysed solutions of 3 and 4 containing small amounts of an additional photolabile diene as a control compound, and examined the photolysate after ca.…”

Section: Figmentioning

confidence: 99%

“…A potential problem of particular significance in studies of this type is the lability of 5 and 6 towards direct photoisomerization (20). Thus, it is particularly important to rule out secondary diene photolysis as a contributor to the apparent non-stereospecificity with which 3 and 4 undergo photochemical ring opening (1). Such problems can be minimized by working with solutions of high optical density at the excitation wavelength, and monitoring the progress of the photolyses at very low conversions, as has been done in the present study.…”

Section: Uv Absorption Spectroscopymentioning

confidence: 99%

“…The absence of conjugating substituents to mixtures of all three geometric isomers of 2,4-hexadiene appears to be a general requisite for ring opening to occur except (eq. [ 11 ) (1). The two isomers afford d i f f~~e n t mixtures of the 2,4-hexadienes, in both cases weighted in favour of the formally forbidden isomers that would be formed by the conrotatory was published, an additional report that illustrates the nonstereospecificity of the process in simple systems has appeared (9).…”

Section: Introductionmentioning

confidence: 99%

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Cyclobutene photochemistry. Substituent and wavelength effects on the photochemical ring opening of monocyclic alkylcyclobutenes

Leigh¹,

Zheng²,

Clark³

1990

Can. J. Chem.

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. Can. J. Chem. 68, 1988Chem. 68, (1990. The photochemical ring opening of cis-and trans-3,4-dimethyl-, 1,3,4-trimethyl-, and 1,2,3,4-tetramethylcyclobutene (1,3, and 4, respectively) has been investigated in hydrocarbon solution with 193 nm and 214 nm light sources. Ring opening is non-stereospecific in all cases at both wavelengths. The ratio of dienes formed by the formally allowed to formally forbidden pathways in the photolysis of these compounds is highest (ca. 2) for the trimethylcyclobutenes, and approximately 1 for both cis and trans isomers of the di-and tetramethylcyclobutenes with 193 nm excitation. The diene distributions from photolysis of all compounds but cis-3 show slight wavelength dependence. Gas-and solution-phase UV absorption spectra are reported for 3 and 4, and indicate that there are at least three singlet excited states accessible in the 185-230 nm region in these molecules. The .rr,R(3s) state is the lowest energy state in the gas phase in 3 and 4. The results verify that orbital symmetry factors do not play a role (or a consistent one, at least) in controlling the stereochemistry of the reaction, but they do not allow a firm assignment of the excited state(s) responsible for ring opening. Direct photolysis of these compounds also results in fragmentation to yield . .Z-2-butene (from cis-3 and 4) or E-2-butene (from trans-3 and 4) in addition to propyne or 2-butyne. The 2-butenes are formed A part le cas du produit cis-3, la distribution des dibnes est insensible i la longueur d'onde. On a determink les spectres UV des produits 3 et 4 tant en solution qu'en phase gazeuse; ils indiquent qu'il existe au moins trois ttats singulets excitCs accessibles dans la rCgion de 185 i 230 nm de ces moltcules. Pour les composts 3 et 4, en phase gazeuse, 1'Ctat .n,R(3s) possbde 1'Cnergie la plus basse. Les rtsultats confirment que les facteurs de symCtrie orbitalaire ne jouent pas un r61e (au moins important) dans le contr6le de la stCrtochimie de la reaction; ils ne permettent toutefois pas dkterminer avec certitude quel(s) est (sont) le(s) Ctat(s) excitC(s) de l'ouverture du cycle. La photolyse directe de ces composts conduit aussi i une fragmentation conduisant au Z-2-butbne (a partir des composts cis-3 et 4) ou au E-2-butbne ( i partir des trans-3 et 4) en plus du propyne ou du 2-butyne. Dans tous les cas, les 2-butbnes se forment avec une sttrtospCcificitt superieure a 90%. Les structures des quatre 3-mtthyl-2,4-hexadibnes isombres qui se forment par photolyse du produit 3 ont Ct C attribukes sur la base de leurs spectres RMN du 'H et des rtsultats de la thermolyse des deux cyclobutbnes isombres.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Figmentioning

confidence: 99%

Section: Uv Absorption Spectroscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cyclobutene photochemistry. Substituent and wavelength effects on the photochemical ring opening of monocyclic alkylcyclobutenes

Leigh¹,

Zheng²,

Clark³

1990

Can. J. Chem.

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Photopericyclic Reactions of Conjugated Dienes and Trienes

Cook

Leigh

2009

Patai's Chemistry of Functional Groups

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Introduction Ground State Conformational Equilibria and E , Z ‐Isomerization The Excited Singlet States of Conjugated Polyenes: UV Absorption and Emission Spectra Singlet State Photochemistry of Conjugated Dienes and Trienes Conclusion

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