Controlling the regioselectivity of the di-π-methane rearrangements of 1,2-naphtho-annelated barrelene derivatives — Solution versus solid-state photochemistry

Abstract

The synthesis of 1,2-naphtho-annelated barrelene derivatives, namely dimethyl-7,12-dihydro-7,12-ethenobenzo[a]anthracene-13,14-dicarboxylate (4a) and dimethyl-7,14-dihydro-7,14-ethenodibenzo[a,j]-anthracene-15,16-dicarboxylate (4b), and the investigation of their photoreactivity in solution and in the solid state is reported. The irradiation of 4a and 4b resulted in regioselective di-p-methane rearrangements to give semibullvalene products; however, the product distribution is inverted upon changing the reaction medium from solution to the solid state. In solution, an a-naphtho-vinyl bridging predominates as the initial photochemical step because of the selective stabilization of the corresponding transition state, as discussed on the basis of the structures of the related biradical intermediates, whereas the solid-state photoreaction is significantly influenced by the steric constraints within the crystal lattice that only allow a b-naphtho-vinyl bridging.Résumé : On a réalisé la synthèse de dérivés condensés 1,2-naphtobarrèlènes, à savoir le 7,12-dihydro-7,12-éthénoben-zo[a]anthracène-13,14-dicarboxylate de diméthyle (4a) et le 7,14-dihydro-7,14-éthénobenzo[a,j]anthracène-15,16-dicarboxylate de diméthyle (4b), et on a étudié leur photoréactivité en solution et à l'état solide. L'irradiation des composés 4a et 4b conduit à des réarrangements di-p-méthane régiosélectifs et à la formation de produits semibullvalènes; toutefois, la distribution des produits est inversée lorsque le milieu réactionnel passe de la solution à l'état solide. En solution, un pont a-naphtovinyle prédomine comme étape photochimique initiale en raison de la stabilisation sélective de l'état de transition correspondant, tel que discuté sur la base des structures des intermédiaires biradicalaires apparentés, alors que la photoréaction à l'état solide est fortement influencée par des contraintes stériques dans le réseau cristallin qui ne permettent que la formation d'un pont b-naphtovinyle.Mots-clés : réarrangement di-p-méthane, dérivés du barrèlène, photochimie à l'état solide.[Traduit par la Rédaction]

Visible‐Light‐Induced Di‐π‐Methane Rearrangement of Dibenzobarrelene Derivatives

“…Thus, the photoreaction of 1 e – 1 g in the presence of Ir(ppy) 3 gave also the products 2 e – 2 g with the same high regioselectivity as the direct irradiation (Schemes and ). Similarly, the photocatalyzed DPM rearrangement of the naphtho‐annelated barrelene derivatives 1 h and 1 i gave mixtures of the regioisomers 2 h / 2 h′ and 2 i / 2 i′ in a ratio of 87 : 13 and 88 : 12 (Scheme 3), that essentially match the reported ones for direct irradiation (88 : ) …”

Unraveling the Solid-State Photoreactivity of Carbonylbis(4,1-Phenylene)dicarbonazidate with Laser Flash Photolysis

“…The crystal lattice thus provides a unique spatial arrangement that controls the selectivity of solid-state reactions. − The selectivity of solid-state photoreactions is attractive for synthetic applications, , and this concept has been exploited for the selective formation of some natural products. − Furthermore, solid-state photoreactions are both environmentally friendly and sustainable because they do not require solvents and can be driven by sunlight or energy-efficient light-emitting diodes. , However, there are several reactions that exhibit selectivity in the solid state lower than that in solution. Although these reactions are generally not synthetically useful, they can provide insight into how the crystal lattice impedes some reactions but facilitates others. − …”

Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives

“…Moreover, additional functionalities, e.g., hydroxy or amino groups, may be attached to the benzene rings of the semibullvalene structure to enable additional hydrogen bonding with the substrate. Also, the benzene rings may be further annelated with additional aromatic units to increase the potential π-stacking area [ 13 ]. Most notably, dibenzosemibullvalenes are chiral compounds, so that the propensity of an enantiopure pyDBS derivative to act as phase-transfer catalyst in stereoselective reactions may be considered in long-term studies.…”