Photochemical addition of acyclic 1,3-dienes to 9-cyanoanthracene and 9-anthraldehyde, a 4.pi. + 2.pi. stereospecific photochemical cycloaddition

Diels–Alder reactions of anthracene, 9-substituted anthracenes and 9,10-disubstituted anthracenes

“…No Diels -Alder adducts were noted in these reactions, but subsequent studies using 9-substituted anthracene derivatives obtained stereospecific photochemical [4þ2] cycloaddition products along with small amounts, of the anthracene dimer. 153 It was postulated that the stereospecificity observed in these reactions suggested that the course of the photochemical addition reaction may be controlled by the configuration of the reacting components in an exciplex intermediate.…”

Chemistry of exciplexes. IV. Orientation of photocycloaddition of 1,3-dienes to anthracenes

“…The conservation of orbital symmetry plays an important role in the orientation of cycloadditions between unsaturated systems. The Woodward-Hoffmann rule of conservation of orbital symmetry predicts that suprafacial photocycloadditions involving An -electrons are allowed processes while those involving 4« + 2 -electrons are forbidden.1 Anthracene reacts photochemically with either 2,5-dimethyl-2,4-hexadiene (DMHD), an acyclic s-transoid 1,3diene, or 1,3-cyclohexadiene (CHD), an alicyclic s-cisoid 1,3-diene, to give 4 5 + 4 8 adducts la and 2a, respectively, while 9-cyanoanthracene under similar conditions reacts with CHD to give the 4 $ + 4 $ adduct 2e but with acyclic s-transoid 1,3-dienes to give 4 $ + 2 $ adducts such as 3e.2 3 The photocycloadditions of DMHD and other s-transoid 1,3-dienes to 9-cyanoanthracene constitute an "apparent forbidden" process according to the Woodward-Hoffmann rule, yet they proceed stereospecifically and regiospecifically in both high chemical and quantum yields.3 Several explanations have been proposed for the orientation of these photocycloadditions,3-5 but no systematic correlations have been presented so far. In our investigation on the nature and behavior of [arene*: 1,3-diene] exciplexes, we studied simultaneously the exciplex fluorescence6 and photochemistry of substituted anthracenes with 1,3-dienes.…”

Photochemistry of diaryl ketones: a new photocyclization reaction

“…Mechanism. Saltial et al,13,14 Lewis and Hoyle,15 and Yang et al [16][17][18] have shown that in some of their systems exciplex formation is solvent dependent and that in these cases exciplex formation is reversible, maximum in case of alcohols and insignificant in case of acetonitrile.…”