Photochemistry of phenyl alkyl ketones under pressure. Reactions of 1, 4-diradicals (original) (raw)
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J Am Chem Soc, 1971
The photolysis in benzene of endo-5-benzoylbicyclo[2.1 .l]hexane (5) has been found to afford A3-cyclopentenylacetophenone (7) and 2-pheny1tricyclo[3.2.0.03~7]heptan-2-ol (8). Tricyclic alcohol 8 was found to rearrange thermally to A3-cyclopentenylacetophenone. In the presence of 90 x acetic acid, tricyclic alcohol 8 rearranged to give 2-phenyl-2-norbornen-exo-6-01 (ll), 2-phenyl-6-exo-acetoxy-2-norbornene (12), 2-phenyltricyclo-[2.2.1 .02 ?6]heptan-3-01 (13), and 2-phenyl-3-acetoxytricyclo[2.2.1 .0*t6]heptane (14). The photochemical transformations encountered in this work appear to be best described by a transannular hydrogen abstraction followed by subsequent reactions of the diradical thus formed. The photoreactions were shown to proceed by way of a triplet n-a* state. In striking contrast to the extraordinarily slow cyclobutylphenyl ketone system, both exo-and endo-5-benzoylbicyclo[2.1 .l]hexanes were found to rearrange at a faster rate than valerophenone. The inefficiency of these reactions (CP exo = 0.06, CP endo = 0.20) can be attributed to an unusually rapid triplet degradation. n the preceding paper, it was shown that the irradia-
Journal of the American Chemical Society, 1971
Mechanistic studies on the photorearrangements of benzobicyclo[2.2.2]octadienone (1) and bicyclo-[2.2.2]octenone (5) are reported. The limiting quantum yields for the singlet reaction of 1 are: &is = 0.50; @nsphthslene = 0.45; ~4,5-benLobie,c~o[l.l.0100ta-2,1-dion.8~0~~ = 0.10. The limiting quantum yields for the acetophenonesensitized reaction are: adis = 0.14; anaphthslene = 0.01 ; ~b e n r o t r i o y e l o [ 3 . 3 . 0 , 0 2~8~~~t e n~3 . 0 n e = 0.12. A deuterium labeling experiment established the 1,2-acyl migration mechanism for the photosensitized rearrangement of 1. Finally, it was shown that the triplet reaction proceeded by a concerted, symmetry-allowed process by comparison with the photoisomerization of lactone 12.
High Pressure Photochemistry of Alkenes. 6. the Case of 1-Methylcyclopentene At 184.9 and 147.0 nm
Research on Chemical Intermediates - RES CHEM INTERMEDIATES, 1989
The degradation of the 184.9 nm photoezcited 1-methyl-l-cyclopentene molecule shows the involvement of various excited isomers. The most important fragmentation products are 1-and 2-methyl-l,8-cyclopentadiene. These products are probably the result of a one-step elimination process of a hydrogen molecule. This process has also been observed in the case of the 18(.9 nm photochemistry of cyelopentene. On the other hand, the involvement of isomers, although possible, is not so obvious at 147.0 nm. Moreover, in this case, the 1-and 2-methyl-l,8cyclopentadiene formation is the result of hydrogen atom elimination in a two-step process. Cyclopentadiene, ethylene, and various C3 and C4 compounds are formed as well as methyl radicals and hydrogen atorr~. These products are probably formed in successive elimination reactions as this is also observed in aeyelie alkenes. 0922-6168/89/$03.50 9 1989 Elsevier Science Publishers B.V.
Journal of Organic Chemistry, 1985
The thermolysis and 350-nm and 185-nm photolyses of the azoalkanes 2,3-diazabicyclo[2.2.l]hept-2-ene (la) and spiro[cyclopropane-1,7'-[2,3]diazabicyclo[2.2.l]hept-2-ene] (lb) have been investigated. The exo/endo stereochemistry in the bicyclo[2.l.Q]pentanes 2a,b and in the rearranged olefin 3b w a~ determined by deuteration experiments using 5,6-exo-dideuterioazoalkanes la,b-d2. Whereas thermal and direct photochemical (350 nm; n, T * ) denitrogenation of azoalkane la-d2 led exclusively (>99%) to bicyclo[2.1.0]pentane 2a-dz with preferential (1.54, 2.94) double inversion, the triplet-sensitized photolysis afforded nearly complete stereoequilibration. In 185-nm denitrogenation an unexpectedly high exo/endo ratio (3.1) for bicyclo[2.1.O]pentane 2a-d, was found, besides isomerization to cyclopentene 2a-dz. Similar results were obtained in the denitrogenation of spiroazoalkane lb-d2, which exhibited exo stereochemical preferences in both photoproducts spiro[bicyclo[2.1.0]pentane-5,1'cyclopropane] 2b-d2 and bicyclo[3.2.0]hept-l-ene 3b-d2. The 350-nm photolysis of azoalkane lb-d, gave preferential formation of ezo-spirobicyclo[2.1.O]pentane 2b-d2 and exo-olefin 3b-d2, whereas triplet-sensitized decomposition yielded almost complete loss of stereochemical preference in the olefin 3b-dz. The 185-nm photolysis of azoalkane lb-d2 showed similar behavior compared with the azoalkane la, e.g., a t high exo/endo ratio in spirobicyclo-[Z.l.O]pentane 2b-d2. Also olefin 3b was formed with complete stereoequilibration. These diverse experimental results are discussed in terms of one-bond vs. two-bond cleavage processes leading to the diazenyl diradicals D'n,,,
Organic Reactions at High Pressure: Cycloaddition Reactions of 11-Methylene-1,6-methano[10]annulene
Angewandte Chemie International Edition in English, 1986
The (R,S)-aminal 3 , prepared from glycine methyl ester hydrochloride, methylamine, and pivalaldehyde,l'"l was treated with 14 chiral carboxylic or sulfonic acids. In two cases one of the two possible diastereomeric salts crystallized selectively: the salt from ( -)-2,3 :4,6-di-O-isopropylidene-2-ketogulonic acid [( -)-diacetone-2-ketogulonic acid] and ( S ) -3 , and that from (S)-( -)-mandelic acid and ( R ) -3 . For preparative resolution a single crystallization with mandelic acid gave enough enrichment so that N-benzoylation and recrystallization of 2 produced the two enantiomers with greater than 98% ee. Mandelic acid is recovered in 95% yield without detectable racemization.
Canadian Journal of Chemistry, 1985
We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and...
2002
The rate constants for the quenching of indane-1,2,3-trione (1) and 5-methoxyindane-1,2,3-trione (2) triplets by olefins, in degassed benzene solution, have been measured by laser flash photolysis. The alkenes studied included acyclic, cyclic, isolated and conjugated dienes, and enol ethers. No quenching was observed when irradiation was performed in the presence of olefins substituted with electron-accepting groups such as maleic anhydride, dimethyl fumarate, dimethyl maleate or chalcone. The plots of log kq versus the ionization potential for cyclohexene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2,3-dimethylbut-2-ene, trans-penta-1,3-diene, ethyl vinyl ether and ethyl prop-1-en-1-yl ether are linear with a slope of -2.7/eV (r = 0.98) for 1 and -2.6/eV (r = 0.95) for 2. The magnitude of the slope is in agreement with a mechanism involving a partial charge transfer complex, which then leads to product formation. A comparison of the reactivity of 1 and 2 toward olefins shows that a similar mechanism operates for the quenching processes of these two triketones.