Photoinduced Aerobic Iodoarene‐Catalyzed Spirocyclization of N‐Oxy‐amides to N‐Fused Spirolactams**

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 the eighties, before witnessing a dramatic surge in the 2000's. 2-4 They possess many advantages in terms of versatility, high selectivity and lack of toxicity; however, their use as a stoichiometric reagent remains a drawback. Indeed, the driving force behind their reactivity is the final release of one equivalent of iodoarene (Scheme 1a), such as iodobenzene. The liberation of a stoiC 50 and HFIP-derived D (Scheme 5b). For Kita's bis iodoarene catalyst, 38 the stabilization would come from the formation of µ-oxo species. CONCLUSION: Using the spiro-cyclization of amides as a model reaction, we have demonstrated that aerobic iodoarene catalysis can be enabled by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalyst under very mild operating conditions. We are currently pursuing more thorough study of this dual catalyst system to gain a deeper understanding of the reaction parameters by experimental and theoretical methods. This will allow us to expand the range of transformations that can be accomplished using this strategy, including the development of asymmetric reactions. ASSOCIATED CONTENT Supporting Information includes, optimization studies and control experiments, detailed synthetic procedures, characterizations of the compounds and copies of the NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

Iodine–Iodine Cooperation Enables Metal-Free C–N Bond-Forming Electrocatalysis via Isolable Iodanyl Radicals

“…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 …”

“…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.…”

“…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.…”

Progress in organocatalysis with hypervalent iodine catalysts

“…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.…”

Rapid synthesis of spirodienones via electrochemical dearomative spirocyclization in flow

“…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…”