Manganese‐Dioxide‐Catalyzed Trifluoromethylation and Azidation of Styrenyl Olefins via Radical Intermediates

Abstract

Am anganese-dioxide-catalyzed trifluoromethylation of styrenes and enol acetates using the Langlois reagent is reported. Employing oxygen/air as the oxidant, styrenes afforded am ixture of the trifluoromethylacohol and ketone products in good overall yields. The protocol also works successfully for converting a-methylstyrened erivatives to the corresponding trifluoromethyl alcohols. The keto-trifluoromethylated products could be obtained exclusively when using enol acetates as substrates under the same reaction conditions. The method was extended to the radical azidationo fe nol acetates using trimethylsilyl azide to furnish the corresponding azido-ketones in good yields.Catalytic strategies for olefin functionalization form av ersatile repertoire of reactions using whichadiversea rray of functionalities can be generated. [1] The applicationo ff irst row transition metal catalysts forf unctionalization of olefins via free radical pathways has been an attractive synthetic pathway to explore, as demonstrated by recently reported elegant studies. [2] Amongt he many challenges, the controlo fo xidation state outcome, application of minimally functionalized olefins, and the development of inexpensive catalyst systems remaina tt he forefront. In this context,t he trifluoromethylation of olefins has been studied extensively with many catalysts including Cu, [3] Fe, [4] Pd, [5] Ag, [6] Ru, [7] and photoredox systems. [8] Oxidative trifluoromethylations employing as ilver catalystw ith various oxidants have also been reported. [9] Given the rich chemistry of manganese in Nature as well as in synthetic systems, [10] we were interestedi nd eveloping radicalt rifluoromethylation [11] and azidation [2k, 12] of olefins using readily available reagents and inexpensivec atalyst [2a, j, k, 13] which could operate in conditions that didn ot involve stoichiometrica mountso fa dditives [2a, b] and oxidants such as peroxides. [2c, 14] We selected vinyl naphthalene for optimizations tudy and performed variouse xperiments to ascertain the best condi- [a] Scheme1.Oxytrifluoromethylation reaction scope.Reactionconditions: styrenederivative (1 equiv.), CF 3 SO 2 Na (2 equiv.), MnO 2 (0.2 equiv.), and K 2 S 2 O 8 (0.2 equiv.) werec ombined in DMF (2 mL) and stirreda tr tf or 6-24 hours.Scheme2.Reactionscope: a-methylstyrenes. Isolated yields are reported.[a] Reaction performed under air.

Visible-Light-Mediated Amination of π-Nucleophiles with N-Aminopyridinium Salts

“…Addition of radicals to enols represents a convenient method for the synthesis of α-substituted ketones. This approach has been adopted for practical alkylations, 28 trifluoromethylations [29][30] and other fluoroalkylations, [31][32][33] oxyamination, 34 and azidation. 30 Knowing that N-protected aminopyridinium salts are a source of electrophilic N-centered radicals, we thought that they could be trapped by enol equivalents giving access to α-amino-carbonyl compounds.…”

Visible-Light-Mediated Amination of π-Nucleophiles with N-Aminopyridinium Salts

“…This approach has been adopted for practical alkylations, 28 trifluoromethylations 29-30 and other fluoroalkylations, [31][32][33] oxyamination, 34 and azidation. 30 Knowing that N-protected aminopyridinium salts are a source of electrophilic N-centered radicals, we thought that they could be trapped by enol equivalents giving access to α-amino-carbonyl compounds.…”

Chemical versatility of azide radical: journey from a transient species to synthetic accessibility in organic transformations

“…In 2018, metal-catalyzed free-radical oxidative oxyazidation methods for terminal alkenes have been reported by various groups to access a-azidoketones by utilizing molecular oxygen. Singh et al 104 used MnO 2 catalyst for aryl enol acetates as the substrate, whereas the Xiong group 105 utilized the Cu(OTf) 2 catalyst for styrenes. However, these methods are not generalized in terms of substrate scope and require metal catalysts.…”