22183-20-6Relevant academic research and scientific papers
Paracyclophanes. Part 58 [1]. On the use of the stilbene-phenanthrene photocyclization in [2.2]paracyclophane chemistry
Hopf,Hucker,Ernst
, p. 947 - 969 (2008/09/17)
The application of the stilbene→phenanthrene photocyclization to [2.2]paracyclophane chemistry has been investigated. For the model system 4-styryl[2.2]paracyclophane (2) to [2.2]phenanthrenoparacyclophane (3) the reaction allows the introduction of alkyl substituants in the 6-, 7-, 8- and 9-position of the phenanthrene moiety. However, when the substituent in the 9-position (bay area of phenanthrene nucleus) becomes too large, viz. tert-butyl, no ring closure is observed anymore. The side products of the process (ring cleavage products of the cyclophane core such as 9 and 10) have been characterized for the first time. Extension of the condensed deck is possible leading to PAH-phanes as demonstrated by the preparation of the chrysenophanes 45 and 60; the cyclization to novel helicenophanes such as 50 also takes place without difficulties. In the case of 1,2-di(4-[2.2] paracyclophanyl)ethene (63) the triply-layered hydrocarbon 65 is produced on irradiation in small amounts.
Photocyclization of 2,4,6,2′,4′,6′-hexaalkylbenzils
Wagner, Peter J.,Park, Bong-Ser,Sobczak, Martin,Frey, Joseph,Rappoport, Zvi
, p. 7619 - 7629 (2007/10/02)
Three of the title compounds - the hexamethyl-, hexaethyl-, and hexaisopropylbenzils - all photocyclize both in solution and as solids to 5,7-dialkyl-2-(2′,4′,6′-trialkylphenyl)-2-hydroxy-1-indanones. At wavelengths 4. Moreover, AM1-level semiempirical calculations suggest that a simple exothermic hydrogen transfer can convert the 1,4-biradical triplet dienol to the same 1,5-biradical formed by δ-hydrogen abstraction. The 1,5-biradical has two major conformations, one leading to Z product and an internally OH-O=C hydrogen bonded one leading to E product. The AM1 computations suggest that the two conformations are of comparable energy and thus implicate 1,5-biradicals as the major precursors to hydroxyindanone products. Stern-Volmer quenching studies indicate a triplet decay rate of 5 × 106 s-1 for the hexaisopropylbenzil. The known behavior of structurally similar monoketones predicts such a rate for δ-hydrogen abstraction but a much slower rate for γ-hydrogen abstraction. However, relative quantum efficiencies parallel those for benzocyclobutenol formation from 2,4,6-trialkylbenzophenones (iPr and Et ～0.3, Me ～0.03). The hexa-tert-butylbenzil undergoes very low quantum yield formation of 3,3-dimethyl-5,7-di-tert-butyl-1-indanone and 2,4,6-tri-tert-butylbenzaldehyde, presumably by δ-hydrogen abstraction and highly efficient radical cleavage of the resulting 1-aroyl-1-indanol.
