Bromonium salts: diaryl-λ³-bromanes as halogen-bonding organocatalysts

Abstract

Bromonium salts have been typically but infrequently used in various reactions as good leaving groups or as aryl or vinyl transfer reagents owing to their extremely high nucleofugality. Herein, we...

Cyclic Diaryl λ3‐Bromanes as Original Aryne Precursors

“…While the rare literature known protocols to access diaryl λ 3 ‐bromanes are low‐yielding, require several steps and harsh reaction conditions, [10, 11] we surmised that 2 a might be afforded efficiently from 1 a via a single oxidation step while using finely selected oxidant and Brønsted acid (Figure 2). Rewardingly, while reacting, under mild conditions, 1 a with t BuONO and MeSO 3 H, the desired compound 2 a ‐OMs was isolated in 93 % yield.…”

“…[7] Accordingly, superior nucleofugality of λ 3 ‐bromanes was witnessed in the arylation [8] reactions while sulfonylimino‐λ 3 ‐bromanes turned out to be potent aminating agents, mediating transition metal‐free C(sp 3 )‐H activation of simple alkanes [9] . Very recently, cyclic hypervalent λ 3 ‐bromide has been also engaged as Lewis‐acid organo‐catalyst for Michael reactions [10] . Despite the unique intrinsic properties of λ 3 ‐bromanes, the lack of efficient protocols to prepare them has limited the development of this research field.…”

“…This reactivity, implying formal C À H functionalization, occurring under mild reaction conditions and obviating need of fluorinating agents, is arguably amongst the most appealing and general routes furnishing arynes. [16] While the rare literature known protocols to access diaryl l 3 -bromanes are low-yielding, require several steps and harsh reaction conditions, [10,11] we surmised that 2 a might be afforded efficiently from 1 a via a single oxidation step while using finely selected oxidant and Brønsted acid (Figure 2). Rewardingly, while reacting, under mild conditions, 1 a with tBuONO and MeSO 3 H, the desired compound 2 a-OMs was isolated in 93 % yield.…”

“…[9] Very recently, cyclic hypervalent l 3 -bromide has been also engaged as Lewis-acid organo-catalyst for Michael reactions. [10] Despite the unique intrinsic properties of l 3 -bromanes, the lack of efficient protocols to prepare them has limited the development of this research field. While thermal decomposition of diazonium salts in presence of aryl bromide furnished l 3 -bromane as early as 1952, [11] harsh reaction conditions and low yields hampered further progress.…”

“…Moreover, the angle between C1-Br1-C12 is 86.93(9)8 reflects a T-shape structure typical for three-centered-four-electron (3c-4e) bonding. [10,16,18] The generality of this protocol delivering diaryl l 3 -bromanes was further surveyed (Figure 2). First, compatibility of this reaction with various acids was confirmed, thus delivering 2 a with different counter anions in excellent to moderate yields (93 % to 29 %).…”