Abstract:We report that the spirocyclization of N-oxy-amides to N-fused spirolactams can be achieved under photoinduced aerobic conditions, using a dual iodoarene/pyrylium catalytic system. 13 spirolactams were obtained in this manner and control experiments have shown that the reaction does not proceed if either one of the catalyst is omitted or in the absence of light and/or oxygen. INTRODUCTION: Hypervalent iodine(III) compounds have been known for 130 years, 1 yet interest in their reactivity was very modest until … Show more
“…1 H NMR (δ, 23 °C, 400 MHz, CDCl 3 ): 6.94 (d, J = 10.2 Hz, 2H), 6.37 (d, J = 10.1 Hz, 2H), 6.14 (s, 1H), 2.70 (t, J = 7.9 Hz, 2H), 2.38 (t, J = 8.0 Hz, 2H), 2.14 (s, 2H). The obtained spectral data were in good agreement with the literature …”
Section: Methodssupporting
confidence: 89%
“…The obtained spectral data were in good agreement with the literature. 20 Lactonization of 6 Catalyzed by 1a. A 10 mL glass vial was charged with 6 (39.8 mg, 0.201 mmol, 1.00 equiv), 1a (0.101 mmol, 5 mol %), tetramethylammonium acetate (57.0 mg, 0.401 mmol, 1.99 equiv), tetrabutylammonium hexafluorophosphate (390 mg, 1.01 mmol, 5.02 equiv), and hfip (5.0 mL) and was fitted with a glassy carbon anode, platinum cathode, and Ag + /Ag reference electrode.…”
Section: ■ Experimental Sectionmentioning
confidence: 99%
“…Organic hypervalent I(III) and I(V) reagents are commonly encountered oxidants in fine-chemical synthesis that operate via selective two-electron oxidation–reduction processes. The potential role of iodanyl radicals ( i.e., formally I(II) species) in substrate functionalization chemistry is far less explored. − Recently, transient iodanyl radicals have been proposed as intermediates in the photochemistry of I(III) compounds and as intermediates in aerobic and electrochemical syntheses of I(III) derivatives. ,− For example, in 2020, we reported an electrochemical C–H/N–H coupling catalyzed by iodoanisole that was proposed to proceed via carboxylate-stabilized iodanyl radicals . While increasingly invoked, the complete lack of isolable organic I(II) compounds has prevented interrogation of potential reactions of these open-shell species toward substrates.…”
Small molecule redox mediators convey interfacial electron transfer events into bulk solution and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here, we report that 1,2-diiodo-4,5-dimethoxybenzene is an efficient electrocatalyst for C−H/E−H coupling that operates at as low as 0.5 mol % catalyst loading. Spectroscopic, crystallographic, and computational results indicate a critical role for a three-electron I−I bonding interaction in stabilizing an iodanyl radical intermediate (i.e., formally I(II) species). As a result, the optimized catalyst operates at more than 100 mV lower potential than the related monoiodide catalyst 4iodoanisole, which results in improved product yield, higher Faradaic efficiency, and expanded substrate scope. The isolated iodanyl radical is chemically competent in C−N bond formation. These results represent the first examples of substrate functionalization at a well-defined I(II) derivative and bona f ide iodanyl radical catalysis and demonstrate one-electron pathways as a mechanistic alternative to canonical two-electron hypervalent iodine mechanisms. The observation establishes I−I redox cooperation as a new design concept for the development of metal-free redox mediators.
“…1 H NMR (δ, 23 °C, 400 MHz, CDCl 3 ): 6.94 (d, J = 10.2 Hz, 2H), 6.37 (d, J = 10.1 Hz, 2H), 6.14 (s, 1H), 2.70 (t, J = 7.9 Hz, 2H), 2.38 (t, J = 8.0 Hz, 2H), 2.14 (s, 2H). The obtained spectral data were in good agreement with the literature …”
Section: Methodssupporting
confidence: 89%
“…The obtained spectral data were in good agreement with the literature. 20 Lactonization of 6 Catalyzed by 1a. A 10 mL glass vial was charged with 6 (39.8 mg, 0.201 mmol, 1.00 equiv), 1a (0.101 mmol, 5 mol %), tetramethylammonium acetate (57.0 mg, 0.401 mmol, 1.99 equiv), tetrabutylammonium hexafluorophosphate (390 mg, 1.01 mmol, 5.02 equiv), and hfip (5.0 mL) and was fitted with a glassy carbon anode, platinum cathode, and Ag + /Ag reference electrode.…”
Section: ■ Experimental Sectionmentioning
confidence: 99%
“…Organic hypervalent I(III) and I(V) reagents are commonly encountered oxidants in fine-chemical synthesis that operate via selective two-electron oxidation–reduction processes. The potential role of iodanyl radicals ( i.e., formally I(II) species) in substrate functionalization chemistry is far less explored. − Recently, transient iodanyl radicals have been proposed as intermediates in the photochemistry of I(III) compounds and as intermediates in aerobic and electrochemical syntheses of I(III) derivatives. ,− For example, in 2020, we reported an electrochemical C–H/N–H coupling catalyzed by iodoanisole that was proposed to proceed via carboxylate-stabilized iodanyl radicals . While increasingly invoked, the complete lack of isolable organic I(II) compounds has prevented interrogation of potential reactions of these open-shell species toward substrates.…”
Small molecule redox mediators convey interfacial electron transfer events into bulk solution and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here, we report that 1,2-diiodo-4,5-dimethoxybenzene is an efficient electrocatalyst for C−H/E−H coupling that operates at as low as 0.5 mol % catalyst loading. Spectroscopic, crystallographic, and computational results indicate a critical role for a three-electron I−I bonding interaction in stabilizing an iodanyl radical intermediate (i.e., formally I(II) species). As a result, the optimized catalyst operates at more than 100 mV lower potential than the related monoiodide catalyst 4iodoanisole, which results in improved product yield, higher Faradaic efficiency, and expanded substrate scope. The isolated iodanyl radical is chemically competent in C−N bond formation. These results represent the first examples of substrate functionalization at a well-defined I(II) derivative and bona f ide iodanyl radical catalysis and demonstrate one-electron pathways as a mechanistic alternative to canonical two-electron hypervalent iodine mechanisms. The observation establishes I−I redox cooperation as a new design concept for the development of metal-free redox mediators.
“…Furthermore, photoredox catalysis was employed for the dearomatisation of p -substituted anisole derivatives 384 to spirolactams 387 under blue light irradiation. 209 Photoredox catalyst 386 and iodoarene 385 used were mesityl-2,6-diphenylpyrylium tetrafluoroborate (MDPT) and Kita's catalyst, respectively. The substrates with electron-withdrawing groups and those groups capable of stabilising a putative radical intermediate on nitrogen were found ineffective while electron-rich groups were tolerated successfully.…”
“…The extra incorporation of sacrificial chemical oxidants enables the catalytic variants possible, including even catalytic asymmetric transformations. 8 The productive interplay of hypervalent iodide catalysis with electrosynthesis 9 and photosynthesis 10 further pushes the boundaries of dearomative spirocyclization to the realm of green chemistry. 11…”
Preparation of the biologically relevant spirodienones from arenol derivatives is typically performed in batch using superstoichiometric oxidants. Herein, we have developed an electrochemical dearomative spirocyclization in flow, featuring the use...
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