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Scientific article
English

Photochemical and thermal rearrangements of a benzoylnaphthobarrelene-like system

Published inTetrahedron, vol. 37, no. 19, p. 3245-3261
Publication date1981
Abstract

8-Benzoyl-9-deuterionaphtho[de-2.3.4]bicyclo[3.2.2]nona-2,6,8-triene (12a)rearranges in a photochemical di-π-methane-type process to the l-benzoylatho[de-[2.3.4]tricyclo[4.3.0.02,9]nona-3,7-dienes 14a-c.The dihydro derivate 13a and the hydroxypheoylmethyl analogs 21a and 22a undergo similarly regioselective rearrangements to 15a+c, 23a-c, and 24a, respectively. At 298 K the primary photoreaction directly occus from the S1(n,π*) and T2(n,π*) states, and it proceeds from T1(π,π*) and from S2(π,π*) either directly or via T2. At lower temperature on direct irradiation. S1→T intersystem crossing and triplet reaction compete with reaction from the singlet. The rearrangement 12a14a-c proceeds along three reaction paths evolving from the two primary photochemical processes of naphthyl-vinyl and vinyl-vinyl bonding in β-position to the CO (1225+29). Two ground-state triplet diradical intermediates such as 25 and 27 have been shown to intervene consecutively—for the first time in di-π-methane photochemistry. Each has been characterized by ESR and IR, and the second one additionally by fluorescence and fluorescence excitation, and by laser flash photolysis.

The failure of products 14a-c to interconvert photochemically is ascribed to efficient energy dissipation through thermally reversible pbotocleavage of the 3-membered ring.

Compounds 12 and 14 thermally interconvert in the dark which constitutes the first example of a ground-state counterpart of a di-π-methane photorearrangement. The thermal reaction includes a path with highly regioselective (and possibly concerted) product formation competing with a stepwise process causing positional scrambling. The sequence 12→14 (photochemically; Φ = 1.0 at 366 nm and 298 K) and an electrophile-catalyzed reversal 1412 in the dark is a model of a chemical light energy storage cycle which can be conducted without loss of reactants.

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Citation (ISO format)
DEMUTH, Martin et al. Photochemical and thermal rearrangements of a benzoylnaphthobarrelene-like system. In: Tetrahedron, 1981, vol. 37, n° 19, p. 3245–3261. doi: 10.1016/S0040-4020(01)92372-5
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