Thermal addition reactions to benzocyclobutenones studied by flash photolysis

Schiess, Peter; Eberle, Marcel K.; Huys-Francotte, M.; Wirz, Jakob

doi:10.1016/s0040-4039(01)80210-0

Cited by 45 publications

(15 citation statements)

References 12 publications

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“…Table 1 shows quenching rate constants for several quenchers. These values are comparable to those reported for the quenching of the vinylketene 8 (10,48).…”

Section: B) I~ltertnoleculai-reactivitysupporting

confidence: 89%

Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Netto‐Ferreira¹,

Scaiano²

1993

Can. J. Chem.

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. Ketene-enols 4 and 5 have been generated by laser flash photolysis of or-tho-benzoylbenzaldehytle (3) and kinetically and spectroscopically characterized. In benzene or acetonitrile, the E ketene-enol, 4, shows absorption at 340 and 400 nm and a lifetime in excess of 1 ms, whereas the Z ketene-enol, 5 , shows maxima at 360 and 430 nrn and a lifeti~iie of only 1.5 ks. At shorter time scales we observed a weak absorption (A,,,;,, = 580 nm) tentatively assigned to biradical 6 with a lifetime of 140 ns. The E ketene-enol is readily quenched by oxygen, dienophiles, methanol, and water, with quenching rate constants ranging from 3.6 x I O M~. ' s ' (for methanol as a quencher) to 2.2 x 10' M ' s-.' (for diethyl ketomalonate). At high water concentrations (typically > 10 M) a new species, 7 , was detected showing maximum absorption at 5 10 nm and a growth lifetime of 7 ks. In deuterated water and using the same concentration as before we observed a formation lifetime for 7 of 10 ks, which results in an isotope effect of -1.5. It is proposed that 5 is the main precursor for 7 . Steady-state irradiation of 3 in deaerated methanol leads to the formation of dihydroanthraquinone (9). a strongly colored and fluorescent (A,,,,, = 475 nm. T , = 29 ns) species, whereas 3-phenylphthalide (2, R = Ph) is the main product when the irradiation is performed in benzene. Steady-state quenching of product formation by diethyl ketomalonate gives a Stern-Volmer constant of 380 M-' from which we conclude that 5 is the ketene-enol responsible for product formation, in agreement with the laser flash photolysis results. . L'irradiation a I'dtat stationnaire du compose 3 dans le methanol desaCr6 conduit a la formation de la dihydroanthraquinone (9), un composk fortement color6 et fluorescent (A,,,:,, = 475 nm, 7" = 20 ns) tandis que le phthalide de phCnyl-3 (2. R = Ph) est le produit majoritaire lorsque I'irradiation a lieu dans le benzene. Le blocage i I'etat stationnaire des produits obtenus B partir du cdtornalonate d'dthyle donne une constante de Stern-Volmer de 380 M-' qui nous porte B conclure que le composd 5 est le cdtkne-en01 responsable de la for~iiation des produits en accord avec les resultats de la photolyse flash au laser.[Traduit par la rCdaction]

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“…Table 1 shows quenching rate constants for several quenchers. These values are comparable to those reported for the quenching of the vinylketene 8 (10,48).…”

Section: B) I~ltertnoleculai-reactivitysupporting

confidence: 89%

Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Netto‐Ferreira¹,

Scaiano²

1993

Can. J. Chem.

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“…In 1984, Schiess et al. reported the cycloaddition of benzocyclobutenone 85 (Scheme ) with various dienophiles under flash photolysis conditions . Upon UV irradiation in ether, benzocyclobutenone 85 underwent isomerization to vinylketene 86 with a lifetime of 170 ms at room temperature.…”

Section: Photolysis‐induced Ring Openingsupporting

confidence: 78%

“…In 1984, Schiess et al reported the cycloaddition of benzocyclobutenone 85 (Scheme 29) with variousd ienophiles under flash photolysis conditions. [37] Upon UV irradiation in ether,b enzocyclobutenone 85 underwenti somerization to vinylketene 86 with al ifetime of 170 ms at room temperature. Unlike simple vinylketenes, which typically react with electron-rich olefins, 86 acted as ad iene and rapidly formed [4+ +2] cycloaddition products with diazo, activated carbonyl compounds or Michael acceptors, likely driven by forming aromatic ketones.…”

Section: Photolysis-induced Ring Openingmentioning

confidence: 99%

Cyclobutenones and Benzocyclobutenones: Versatile Synthons in Organic Synthesis

Chen

Dong

2016

Chemistry A European J

120

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Cyclobutenones, four-membered ketones bearing an unsaturated carbon–carbon double bond, and their structural sibling benzocyclobutenones, possess unique reactivity. Owing to their inherent high ring strain, such structures readily undergo ring opening under a variety of conditions, including thermolysis, photolysis, and transition metal catalysis, to afford reactive intermediates that can be trapped with nucleophiles, dienophiles, and unsaturated bonds. Their electron-deficient enone moieties are good electrophiles for facile nucleophilic addition. Such properties render cyclobutenones versatile synthons, serving as excellent coupling partners in a vast array of synthetically valuable transformations.

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“…A quick and efficient screening of solvents and reagents is possible to study structure-reactivity relationships or to choose optimal reaction conditions for synthetic purposes. 42 The key cyclization step in Quinkert's elegant stereoselective synthesis of estrone, the photoenolization of an ortho-methylphenyl ketone, was successful only under quite unusual ("seemingly alchimistic") reaction conditions. 43 These conditions were not found by serendipity, but by an extremely clever and deliberate exploitation of, inter alia, previous mechanistic investigations of the parent substrate…”

Section: Intersystem Crossing (Isc) At Biradicaloid Geometriesmentioning

confidence: 99%

Spectroscopic and kinetic investigations of conjugated biradical intermediates

Wirz¹

1984

Pure and Applied Chemistry

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-Several reactive biradical intermediates of photochemical reactions were monitored directly in solution by the technique of kinetic and time-resolved spectrographic laser flash photolysis, and identified with the aid of low-temperature epr and optical spectroscopy, semiempirical calculations, as well as conventional steady-state analyses of product distributions. The focus of this report is on a number of mechanistic questions particular to the behaviour of biradicals and the experimental response obtained with a few selected model systems. Some of the results may be expected to hold as guidelines and/or diagnostic tools of some general value in the field of biradical chemistry. What is a Biradical(oid)?I vividly remember several lively discussions on biradicals which were held at the third IUPAC Symposium on Photochemistry fourteen years ago when I joined the community as a newborn chemist. The chairman noted in his preface to the conference report: 'One of these [informal discussion groups] attempted, without any great success, to reach a common understanding about the use of the term 'diradical', but nevertheless it led to a valuable exchange of ideas."1 It was precisely this confusion of ill-defined words and widely differing views, coupled with a general agreement about the key role of these will-o'-the-wisps in photochemistry, which has attracted me and probably many others. Shortly after this conference, Salem and Rowland have removed many of the basic misconceptions in their classical 'mise-au--point' on the electronic structure of biradicals (= diradicals) from the point of view of quantum theory,2 and Michl has published a lucid and inspiring exposure of his qualitative ideas concerning the formation of biradicals in photochemical reactions.3 Some of the semantic discussions are continuing to date. I shall adhere to a pragmatic d LviLtLon o a bUiadLcic ao a mofecuea& enWi who4e £owe4-t 4Lngee-t and Jlp!eA ta-t nekgLe5 do nat dic,t. b mack mo'Le. tkan faT, 4aj 10 kJ/moL The expression "bOadaIoLd" would then extend this range to say 100 kJ/mol. This definition consciously does not make any statement about kinetic stability. In the MO description, biradicaloids have two approximately degenerate orbitals occupied by a total of two electrons. Normally the corresponding resonance structures have one bond less than requested by the usual rules of valence, but cyclobutadiene, molecular oxygen, and many ions provide exceptions to this statement. 1289

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Thermal addition reactions to benzocyclobutenones studied by flash photolysis

Cited by 45 publications

References 12 publications

Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Cyclobutenones and Benzocyclobutenones: Versatile Synthons in Organic Synthesis

Spectroscopic and kinetic investigations of conjugated biradical intermediates

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