The Photolytic Decomposition of Some Sulfones by an Internally Sensitized Path

The Sulfolene Protecting Group: Observation of a Direct Photoinitiated Cheletropic Ring Opening

“…Using vertical excitation to plot the triplet PECs along the two linear coordinates (see SI, Figures SI‐20 and SI‐21, respectively), we find that T 1 , the only triplet state within the triplet‐energy range of the sensitizers used, is repulsive along the linear conrotatory mode, whereas a barrier is evident along the disrotatory mode. Thus the main product should be the conrotatory product, exactly as has been observed [18] …”

“…Third, the sulfolene protecting group may be used to isomerize dienes, as shown in Figure 5 through two consecutive stereoselective reactions, as we carried out above. We find that, whereas triplet sensitized ring‐opening yields only 75 % of the conrotatory product, [18] the direct irradiation seems to yield exclusively conrotatory product, albeit with some expected degradation due to the high‐energy radiation used. A drawback of the high‐energy radiation needed to excite sulfolene is the risk of inducing cis‐trans isomerization of the formed dienes as well, [50] reducing the stereoselectivity.…”

“…SO 2 photoexpulsion from sulfolene has previously been observed, but is limited to triplet‐sensitized expulsions, [18] or to stepwise reactions forming stable biradical species which decay on to form products [19] . Studies of the triplet sensitized reaction initially indicated that the triplet state deactivates via intersystem crossing (ISC) to a vibrationally excited electronic ground‐state from which expulsion would occur.…”

Exploration of Braverman Reaction Chemistry. Synthesis of Tricyclic Dihydrothiophene Dioxide Derivatives from Bispropargyl Sulfones

“…There are some precedents for the formation of orthoquinonedimethane intermediates from either photochemically or thermolytically induced chelatotrophic extrusion of SO 2 from dihydroisobenzothiophene dioxides,11,12 and so heating the sulfone 17 over the temperature range 180 – 340 °C, as well as irradiation (254 - 300 nm, room temperature), were explored in an attempt to force Diels-Alder cycloaddition of the terminal alkyne. However, in no instance was anything other than returned starting material or uncharacterizable decomposition products observed.…”

Benzosulfones as photochemically activated sulfur dioxide (SO2) donors

“…Previously, benzosulfones have been reported to undergo photolysis in organic media when irradiated with UV light through a radical mechanism to produce cyclobutene as the major product. 32 Thus, the stability of the radical should dictate the propensity of the benzosulfone to undergo photolysis. Our results indicate that photolysis is sensitive to substituent effects.…”