130894-27-8Relevant articles and documents
Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes
Rudolph, Andreas,Weedon, Alan C.
, p. 1590 - 1597 (2007/10/02)
The products of the photochemical reaction of 2-cyclopentenone with 1,6-heptadiene and with vinylcyclopropane have been examined.With 1,6-heptadiene the products were cyclobutanes, which arise from 2+2 photocycloaddition between the cyclopentenone carbon-carbon double bond and one of the two terminal double bonds of the heptadiene.The 1,4-biradical that is an intermediate in this reaction contains a derivative of a 1-hexenyl radical; no products derived from cyclization of this intermediate to a cyclopentenylmethyl radical were observed.With vinylcyclopropane some of the products isolated also arose from 2+2 photocycloaddition; in addition, comparable quantities of products resulting from rearrangement of the intermediate 1,4-biradical were obtained.In this case the initially produced intermediate 1,4-biradical contains a cyclopropylmethyl radical that can rearrange to a homoallylic radical; the products isolated were derived from intramolecular disproportionation in the new 1,7-biradical containing the homoallylic radical.The rate constant for the rearrangement of the cyclopropylmethyl radical to the homoallylic radical is known and was used as a clock to estimate the lifetime of the initially produced 1,4-biradical.The value estimated is of the order of 50 ns.The structures of the products indicate that the initial bonding between the excited cyclopentenone and vinylcyclopropane takes place at both the α-position and the β-position of the enone and not exclusively at the α-position as a recent report claims.
