Photochemistry of ethenobenzocycloheptenones

Synthetic Aspects of the Di-π-methane Rearrangement

“…53 In another study, the direct or sensitized irradiation of ethenobenzocycloheptenones 146 brings about the formation of the corresponding DPM products 147 exclusively. 133 This result shows that for compounds 146 aryl-vinyl bridging is preferred to keto-vinyl bridging. The greater stability of the biradical intermediate 148, resulting from benzo-vinyl bridging, compared to biradical 149, which would have been formed in a keto-vinyl bridging, could explain the results obtained in this study.…”

“…Thus, for instance, sensitized irradiation of the bicyclo[2.2.1]heptenone derivative 144 was reported to give the ODPM product 145 in 62% isolated yield, showing that keto−vinyl bridging takes preference over vinyl−vinyl bridging in this instance. 53 In another study, the direct or sensitized irradiation of ethenobenzocycloheptenones 146 brings about the formation of the corresponding DPM products 147 exclusively . This result shows that for compounds 146 aryl−vinyl bridging is preferred to keto−vinyl bridging.…”

“…However, dienones 160 and 161 under similar reaction conditions give E/Z isomerization and decomposition, respectively , ,,,,,− 20, and 21 . Examples of competition between the DPM and ODPM processes in β,γ-unsaturated aldehydes, as well as competition between the DPM and the aza-di-π-methane (ADPM) rearrangements will be discussed in the following sections.…”

One hundred years of benzotropone chemistry

“…In this context, the cycloaddition of 7-bromo-2,3-benzotropone ( 316 ) to maleic anhydride was reported by Hassner’s group ( Fig. 15 ) [ 148 ]. The direct and sensitized photolysis of the cycloadduct 357 afforded di-π-methane rearrangement product 358 , which was confirmed by X-ray diffraction.…”

“…In the first example, Rennhard’s group realized the cycloaddition of benzotropone 12 with maleic anhydride ( 204 ) to give a tricyclic adduct 207 (in 90% yield) ( Scheme 35 ) [ 141 – 142 ]. Later, Middlemiss’ group also used dienophiles such as maleic anhydride ( 204 ), N -methylmaleimide ( 205 ), and N -phenylmaleimide ( 206 ) to give endo -adducts 207 – 209 [ 148 ]. Furthermore, these ethenobenzocycloheptenones 207 – 209 underwent di-π-methane photo-rearrangement to 210 – 212 exclusively ( Scheme 35 ).…”