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The title compounds undergo regio- and diastereoselective [2+2]-cycloaddition at the olefinic C-C bond on irradiation (350 nm) in the presence of either methacrylonitrile or 2,3-dimethylbuta-1,3-diene, affording hitherto unknown 1-cyclobutylalk-1-yn-3-ones or 1-bicyclo[4.2.0]octylalk-1-yn-3-ones, respectively.
[reaction: see text] Whereas cyclopentenylcarbenes resulting from photocycloaddition of 4-alk-1-ynylcoumarins to 2,3-dimethylbut-2-ene undergo tandem cyclization to hitherto unknown tetracyclic (4-hetera)cyclopent[b,c]acenaphthylenes, the corresponding cyclopentenylnitrenes stemming from 4-cyanocoumarins and the same alkene are converted into tricyclic… (More)
An unprecedented 'carbonyl-O-assisted' 1,3-H atom transfer from a CH2 group to a primary alkyl radical center in 1,4-biradicals, formed in a crossed addition mode in the photocycloisomerization of 4-pent-4-enylcyclohex-2-enones, is discussed.
On irradiation (λ = 350 nm) in neat hex-1-yne, naphthalene-1,2-dione monoacetals 1 afford mixtures of pentacyclic photodimers and up to 25% (isolated yield) of mixed photocycloadducts 2. Careful acidic hydrolysis of the acetal function of 2 gives the title compounds 3, the overall sequence representing a first approach to a (formal) [2 + 2] photocycloadduct… (More)
5,5-Dimethylcyclohex-2-enone (1a) photocycloadds to ethylidenemalononitrile (2a) to give 5-oxobicyclo[4.2.0]octane-7,7-dicarbonitriles with slight preference, in analogy to results already described for light induced reactions between cyclohexenones and acrylonitrile (AN). In contrast, irradiation of 1a in the presence of isopropylidenemalononitrile (2b)… (More)
Both 4H,7H-benzo[1,2-c:4,3-c']dithiin-4,7-dione (3) and 4H,7H-thiino[4,3-f]benzopyran- 4,7-dione (4) were synthesized from 1,2-bis(2-hydroxyethyl)benzene (7). On irradiation (lambda > 390 nm) in acetonitrile the symmetric tricycle 3 affords selectively the two-fold cis-cisoid-cis dimer 10 while the asymmetric tricycle 4 gives a 5:1 mixture of the… (More)