N‐Oxyl‐Radical‐Catalyzed Intermolecular Aminooxygenation of Styrenes and Inter/intramolecular Aminoalkoxylation of Homoallylic Alcohols

Abstract

By taking advantage of the redox cycle between the reductive N‐oxyl radical and its oxidative oxoammonium counterpart, the N‐oxyl‐radical‐catalyzed intermolecular aminohydroxylation of styrenes with N‐fluorobenzenesulfonimide was developed. Various vinyl arenes were aminohydroxylated in moderate to excellent yields with high regio‐ and diastereoselectivities by using environmentally benign H2O as the oxygen source. In addition, the sequential inter/intramolecular aminoalkoxylation of homoallylic alcohols was also achieved under anhydrous conditions, which allowed the exclusive synthesis of pharmaceutically useful 2‐aryl‐3‐amino‐disubstituted tetrahydrofurans.

The Electrophilic Fluorination of Enol Esters Using SelectFluor: A Polar Two‐Electron Process

“…[33] The reaction between 1 and TEMPO leads to complete conversion of 1,a s judged by 19 FNMR spectroscopy,a nd the formation of oxoammonium salt [22]BF 4 (Scheme 10 a) as judged by the comparisono fI Ra nd UV spectra with those of an authentic sample prepared by the reactiono fT EMPO with bleach and tetrafluoroboric acid (Scheme 10 b). [43] The use of TEMPO as a radicalt rap in reactions mediated by 1 is therefore unreliable. However,w hile [ 22]ClO 4 reacts with vinyl azides to form various functionalised products, [44] [22]BF 4 reacts with 8c and 18 to form the corresponding naphthalenes 23 and 24 (Scheme10c).…”

“…Although the reaction did indeed cease completely upon the addition of TEMPO, this was due to the immediate and complete destruction of 1 . The reaction between 1 and TEMPO leads to complete conversion of 1 , as judged by 19 F NMR spectroscopy, and the formation of oxoammonium salt [ 22 ]BF 4 (Scheme a) as judged by the comparison of IR and UV spectra with those of an authentic sample prepared by the reaction of TEMPO with bleach and tetrafluoroboric acid (Scheme b) . The use of TEMPO as a radical trap in reactions mediated by 1 is therefore unreliable.…”

“…Compounds 2 and [22]BF 4 were prepared according to literature methods. [38,43] Analysis NMR characterisation was carried out using Bruker AV3-400 equipped with al iquid nitrogen Prodigy cryoprobe, or aB ruker AV400 equipped with aB BFO-z-ATMA probe;k inetic data were obtained using aB ruker AVII-600 NMR spectrometer equipped with a BBO-z-ATMA probe. All NMR chemical shifts are quoted in units of parts per million (ppm).…”

“…Each batch of SelectFluor ( 1 ) was analysed by iodometric titration and confirmed to be >95 % pure. Compounds 2 and [ 22 ]BF 4 were prepared according to literature methods …”

The Utility of Oxoammonium Species in Organic Synthesis: Beyond Alcohol Oxidation

“…In 2016, Weng and Zhang reported a 4-substituted TEMPO-catalyzed intermolecular aminooxygenation of styrenes and inter/intramolecular aminoalkoxylation of homoallylic alcohols using N-fluorobenzenesulfonimide (NFSI) as an oxidant and aminating reagent. 218 This reaction is based on a similar stoichiometric reaction using TEMPO-Na reported by Studer et al 219,220 The authors accomplished the catalytic transformation using an external nucleophile (H2O and pendant alcohol). In 2017, Zhang et al reported a TEMPO + -mediated tandem cyclization of β-oxoamides with amine hydrochlorides to yield pyrrolin-4-ones.…”