Photochemical behavior of bridged compounds. V. Photochemical transformations of substituted cyclopentadienone dimers (original) (raw)
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Chemical and photochemical behavior of nondissociating cyclopentadienone dimers
The Journal of Organic Chemistry, 1981
The nondissociating character and endo configuration of the substituted cyclopentadienone dimers 2c,d along with the novel "mixed dimers" 2e,f were unequivocally demonstrated. Irradiation of the dimers 2c,d brings about only reversible 1,3-rearrangement to llc,d of all the possible modes available to the system (Scheme IV). In contrast to that, the "mixed dimers" 2e,f undergo only internal cycloaddition to the dissymmetric cage products 6e,f. Stereoelectronic arguments are put forward to rationalize this behavior in a general framework of this class of compounds.
Tetrahedron, 1981
A&ISCI-The I,(dimethyl-. 1.2.~trimethyl and 12.4.7-letramelhyl subslilultd 3.4o.o'~bipbcnykne) cycbpcntodienoncdimcrs ((14 were prepared and found IO undergo phobchcmically or fkrr~//y a 1.3.reananfcmcnl IO [he ccntrosymmetrical diketons (II). Only the tetnmethyl derivative ((r) undergoes al room lempcnlure a hsl. depncrale [X3] Cope reamngemenl wilh AC;,, = Il.4 kcrl md. ' AII these dimers and rearrangement products appear aof IO dissociate IO their monomers. Inn react with dienophilcs IO give the adducts (12, 13). A slcpwiw mechanism involving diradicll inlermcdialcs (19) is invoked. The "mixed dimcr" (II) was also prepared and studied. The stcric and ckclronic cfftc~s determining OK behavtiur of these compounds are discussed. Photocbcmical studies-XX 3ol b&avj~w in cycbaddithn processes. No other features were "13' AI/or of OrpMk Componnh Buttcrworths, London I%6. lluofiomed here. '94. L. AquiIar. M. and A. Maoyarrez_ Boil. Inst. @im. Unb. 9. W. Jones. 1. Cheat Sot. Chtm. Commw 199 (Iws). Nor. Aufor. Ma. 16.40 (1964); Chcm. Abrrr. 0. 1693t (I964). T. I_. C. braoyoviu and J. E. Downcs. BP. 1.052.9Sl clvm "One Sb0dd recall PI his point. lhl "chhcd" non-dissociating Abstr. 64. WZ'le (I%?). dimcrs' consistently hikd to tive adducts of type 12 in heir '9. Fuchs and M. Pastemak. 1. Chum. SM. C&t. Comm. 537 reaction with malcic anhydride. This was adequarely discussed (19n). in Ref. I.
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.
The Journal of Organic Chemistry, 1992
The 3-oxa-1,5-hexadienones 4a, 4b, 5a, and 5b undergo intramolecular [ 2 + 21 photocycloaddition reactions with quantum yields ranging from 0.2 to 0.002. In general, oxa substitution decreases the quantum yields and favors the formation of crossed cloeure producta in comparison to the alkenyl analogs. Irradiation of stereoe~ically deuterated dienones lla and 12a indicate that the intermediate biradical reverts to the starting dienone faster than it proceeds to product. The results are compared with the analogous alkenyl systems. An explanation for changes in regiochemistry, quantum yields, and reversion rates between the two systems is offered.
Tetrahedron, 1980
Irradiation of dissociating cyclopentadienonedimers (2 b,c, e) results in formation of two types of cage-products (5 and 8) in very low quantum yields and good, but wavelength and phase dependent chemical yields, Borh processes are intramolecular; for 2b this was shown using isotopic labeling and massspectrometric techniques. Sensitization and quenching experiments indicate that triplet states are involved. The mechanistic pathways are discussed. The cyclopentadienones(1 b, c, e) were isolated for the first time and irradiation of lb-in the solid gave exclusively-the-symmetric cage (8b).
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, 1994
The regiochemistry of the photochemical cycloaddition reaction between 2-cyclopentenone and the polar alkenes 1,l-difluoroethene and methyl acrylate has been investigated. With 1,l-difluoroethene the major cycloaddition product is a cyclobutane adduct possessing head-to-tail regiochemistry; with methyl acrylate the reaction is nonregioselective and a 46.553.5 ratio of head-to-head and head-to-tail cyclobutane regioisomers is obtained. These regiochemical outcomes are not those predicted by the Corey-de Mayo mechanism conventionally used to describe the enone-alkene photocycloaddition reaction. The triplet 1 ,Cbiradicals implicated as intermediates in the photocycloaddition reaction between 2-cyclopentenone and the polar alkenes methyl acrylate and ethyl vinyl ether have been trapped quantitatively using hydrogen selenide as a hydrogen atom donor. The structures of the trapped products have been determined and hence the structures of their biradical precursors have been inferred. The yields of the trapped biradicals indicate that in both reactions the product distribution is controlled by the extent to which each of the isomeric biradical intermediates closes to products in competition with fragmentation to its ground state precursors. The product distribution does not reflect the relative rates of formation (and hence the relative amounts) of the isomeric biradical intermediates formed in each reaction. This conclusion is inconsistent with the long held idea that an oriented exciplex intermediate controls the reaction regiochemistry by favoring the formation of some biradicals over others. The structures of the biradical intermediates also reveal that both the 2-position and the 3-position of the enone are involved in forming the first bond to the alkene; with ethyl vinyl ether this bond is to the less substituted end of the alkene exclusively, while with methyl acrylate no selectivity in the site of initial bonding is observed.