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Scientific article
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The Synthesis and Photoisomerization of 5-Methyl-5-Vinyl-1,3-Cyclopentadiene

Published inHelvetica chimica acta, vol. 71, no. 2, p. 389-394
Publication date1988-03-16
Abstract

A versatile scheme for the synthesis of geminally disubstituted cyclopentadienes is used to prepare the title compound 4. This remarkably stable vinyl-cyclopentadiene, distinguished by its Cs symmetry, undergoes exclusively electrocyclic ring closure upon direct π–π* excitation at 254 nm. The epimeric vinyl-housenes 11 and 12, which, for geometric reasons, are insensitive to the walk rearrangement, are suggested to be the primary photo-products. One of them, 12, due to its syn-oriented vinyl group, undergoes spontaneous copy rearrangement to give 2-methylbicyclo[3.2.1]hepta-2,6-diene (13). The other, 11, having an anti-oriented vinyl group, can only undergo thermal return to the starting material 4. Whereas no leakage to a 1,5-vinyl migration is discernible for the S1 state of 4, the benzophenone-sensitized photolysis at 350 nm is shown to be governed by this rearrangement. 1-Methyl-5-vinylcyclopenta-1,3-diene (14), the unstable primary product of the sensitized photoreaction, is trapped by 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (PTAD).

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Citation (ISO format)
BURGER, Ulrich, PAMINGLE-CRISTOFORETTI, Eliane, BRINGHEN, Alain Olivier. The Synthesis and Photoisomerization of 5-Methyl-5-Vinyl-1,3-Cyclopentadiene. In: Helvetica chimica acta, 1988, vol. 71, n° 2, p. 389–394. doi: 10.1002/hlca.19880710212
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ISSN of the journal0018-019X
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