PHOTOREARRANGEMENTS OF A NAPHTHOBARRELENE-LIKE SYSTEM - DEPENDENCE ON EXCITED-STATE SPIN MULTIPLICITY AND ELECTRONIC CONFIGURATION, AND EVIDENCE FOR BIRADICAL INTERMEDIATES

8‐Benzoyl‐9‐deuterio‐naphtho [de‐2.3.4]bicyclo [3.2.2]nona‐2,6,8‐triene (1) rearranged quantitatively in a photochemical di‐π‐methane‐type process to 2‐, 6‐, and 9‐deuteriated 1‐benzoyl‐naphtho [de‐2.3.4]tricyclo [4.3.0.02,9]nona‐2, 6‐diene (8a–c). The phenylhydroxymethyl analogue 2 underwent a similar regioselective rearrangement to 9a–c. The rearrangement 1 → 8a–c is proposed to proceed along three reaction paths evolving from two primary photochemical processes of naphthylvinyl and vinyl‐vinyl bonding (1 → 3 + 6). Evidence for a competition between several paths and involvement of biradical intermediates derives from changes in the isotopomeric composition with temperature, and from laser flash detection (λexc 353 nm) of a transient. The dependence of the quantum yield for product formation from 1 on excitation wavelength and sensitizer triplet energy leads to the conclusion that reaction to the primary biradicals occurs directly from the S1 (n, π*) and T2 (n, π* ) states, and that reaction from T1 (π, π*) and from S2 (π, π*) proceed either directly or via T2. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim