Visible-light mediated facile dithiane deprotection under metal free conditions

Combining Photodeprotection and Ligation into a Dual‐Color Gated Reaction System

“…Initial attempts to conduct the wavelength dual‐gated reaction in the absence of bicyclo[2.2.1]hept‐2‐ene as a trapping reagent failed. Although the fragments from the deprotection step were not identified in the present work, it is likely that a free thiol or a disulfide is released [18, 19, 30, 31] . The disulfide is unlikely to influence the Diels–Alder reaction, however a free thiol can react in a thiol‐Michael or thiol‐ene reaction with NEM or with the reactive PE.…”

“…Herein, we combine the photo‐induced deprotection of dithioacetal‐protected aldehyde moieties in the visible wavelength region, [18, 19] with o ‐methylbenzaldehyde activation in the UV region [20–23] . The mechanism of the dithioacetal deprotection, using oxidizing conditions, has been reported previously in the literature [19] .…”

“…Heat was found to favor a partial sulfoxide formation over deprotection (refer to the Supporting Information section 11). Therefore, using a low power LED for the deprotection was important in the current experimental set‐up to minimize thermal heating and afford high conversions [18, 30, 33] …”

PhIO-Mediated oxidative dethioacetalization/dethioketalization under water-free conditions

“…a), The outcome of this isotope-labelling experiment indicates that the oxygen atom of the carbonyl product could be originated from PhIO. Although the previous reports demonstrated that the thio moieties in the substrate was converted to disulfide during the deprotection process, 21,26 dithioacetal 1s was prepared and subjected to the standard conditions to make further corroboration. Unsurprisingly, the reaction of 1s with PhIO in DCM afforded disulfide 3s in 90% yield, with isolation of 4-methylbenzaldehyde 2s in 93% yield (Scheme 4, eq.…”

“…Accordingly, the novel deprotection protocols continuously evolved and now the conversion can be realized by using hydrogen peroxide, 17 oxone, 18 selectfluor, 19 clay 20 and UV/visible light. 21 Furthermore, the electrophilicity of halonium ions also allows the oxidative cleavage of 1,3-dithianes by using halogenation reagents including NBS (N-bromosuccinimide) 22 and NCS (N-chlorosuccinimide). 23,24 It is worth noting that various oxidative systems involving the use of iodine reagents such as NH4I/H2O2, 25 NaI/1,4-benzoquinone (BQ), 26 MeI, 27 I2/H2O2 28 and IBr 29 have also been used for this dethioacetalization process.…”