Mechanism of Hypervalent Iodine Promoted Fluorocyclization of Unsaturated Alcohols: Metathesis via Double Acids Activation

Abstract

Lewis/Bronsted acid activation plays a key role in hypervalent iodine reagent-mediated reactions. In addition to generally accepted cis-activation or trans-activation, this study reveals another important Lewis/Bronsted acid activation mode, the double-activation. Different from the generally proposed iodine­(III)­iranium SN2 mechanism, the hypervalent difluoro-iodoarene-promoted fluorocyclization of unsaturated alcohol prefers to undergo the metathesis mechanism via an iodine­(III)-π intermediate.

Reactions promoted by hypervalent iodine reagents and boron Lewis acids

“…26 Although Lewis/Brønsted acid mediated cis-activation or trans-activation of λ 3 -iodane are common, recently a double-activation mode for hypervalent iodine reagents has also been reported by Liu (Scheme 1). 27 Tricoordinated boron Lewis acids are a popular choice for the activation of hypervalent iodine compounds, such as BF 3 , BAr 3 and borosilicates. Pervasive use of trivalent boron compounds (typically BF 3 ) to activate hypervalent iodine compounds can be explained due to their high Lewis acidity.…”

“…28 Its polymeric zigzag structure with O-I⋯O linkages renders it insoluble in most organic solvents. 27 In 1982, Ochiai and coworkers 29 suggested that BF 3 •OEt 2 activates iodosylbenzene (15) via coordination of the boron Lewis acid to the oxygen atom breaking up the polymeric structure. Analogously, BF 3 •OEt 2 coordination to the acetate oxygen of diacetoxy(m-nitrophenyl)iodane was assumed to activate the λ 3 -iodane at room temperature to effectively oxidise alcohols to carbonyl compounds (Scheme 4).…”

Fluorination and Fluoroalkylation Reactions Mediated by Hypervalent Iodine Reagents

“…The same reaction mechanism observed for ArIF 2 can be addressed by fluoro‐benziodoxoles. Because of their reduced reactivity in comparison with the linear analogs (ArIF 2 ), fluoro‐benziodoxoles have achieved more selective fluorinations with broader functional group tolerance . To meet the growing demands for new fluorine‐18 PET tracers for clinical imaging, the rapid radiosynthesis and application of the electrophilic [ 18 F]fluoro‐benziodoxole reagent from a nucleophilic [ 18 F]F − precursor (e. g., [ 18 F]TBAF) have been presented .…”

Hypervalent Iodine-Mediated Diastereoselective α-Acetoxylation of Cyclic Ketones

“…Metal-free hypervalent iodine compounds as classical oxidative functionalization reagents have attracted considerable interest due to a variety of advantages relative to conventional oxidants such as heavy metals (Pb, Tl, or Hg), including low toxicity, ready availability, mild conditions, excellent selectivity, and a comparable reactivity (Du et al, 2015;Ren et al, 2016;Chen et al, 2017). However, As one of our ongoing interests (Sakamoto et al, 2016(Sakamoto et al, , 2017(Sakamoto et al, , 2018Liu et al, 2017;Selvakumar et al, 2017;Shu et al, 2019) to construct selective methods for α-functionalization of carbonyl compounds, we have become keenly interested in the possibility of the diastereoselective α-acetoxylation of cyclic ketones (Scheme 1C). In this context, we wish to report our initial study on creating a hybrid system comprised of hypervalent iodine(III) reagent and BF 3 •OEt 2 .…”

“…As one of our ongoing interests (Sakamoto et al, 2016 , 2017 , 2018 ; Liu et al, 2017 ; Selvakumar et al, 2017 ; Shu et al, 2019 ) to construct selective methods for α-functionalization of carbonyl compounds, we have become keenly interested in the possibility of the diastereoselective α-acetoxylation of cyclic ketones ( Scheme 1C ). In this context, we wish to report our initial study on creating a hybrid system comprised of hypervalent iodine(III) reagent and BF 3 •OEt 2 .…”