A irradiação na região do ultravioleta de 1,2,3-indanotriona, em presença de 2,3-dimetil-2-buteno, em diclorometano, leva a uma mistura complexa de produtos formados a partir de reações de abstração de hidrogênio, fotocicloadição [2 π +2 π ] (reação de Paternò-Büchi) e fotocicloadição [4 π +2 π ]. A distribuição de produtos é dependente de fatores eletrônicos e estéricos, com estes últimos sendo os responsáveis pelo alto rendimento químico de formação do produto resultante da cicloadição fotoquímica [4 π +2 π ].UV irradiation of 1,2,3-indanetrione, in CH 2 Cl 2 , in the presence of 2,3-dimethyl-2-butene yields a complex mixture of products arising from hydrogen abstraction, [2 π +2 π ] photocycloaddition (Paternò-Büchi reaction), and [4 π +2 π ] photocycloaddition. The reaction is dependent on electronic and steric effects, with the later accounting for the high chemical yield observed for the formation of the dioxene-type product.
The rate constants for the quenching of indane-1,2,3-trione (1) and 5-methoxyindane-1,2,3-trione (2) triplets by olefins, in degassed benzene solution, have been measured by laser flash photolysis. The alkenes studied included acyclic, cyclic, isolated and conjugated dienes, and enol ethers. No quenching was observed when irradiation was performed in the presence of olefins substituted with electron-accepting groups such as maleic anhydride, dimethyl fumarate, dimethyl maleate or chalcone. The plots of log kq versus the ionization potential for cyclohexene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2,3-dimethylbut-2-ene, trans-penta-1,3-diene, ethyl vinyl ether and ethyl prop-1-en-1-yl ether are linear with a slope of -2.7/eV (r = 0.98) for 1 and -2.6/eV (r = 0.95) for 2. The magnitude of the slope is in agreement with a mechanism involving a partial charge transfer complex, which then leads to product formation. A comparison of the reactivity of 1 and 2 toward olefins shows that a similar mechanism operates for the quenching processes of these two triketones.
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