Hg(OTf)₂-Catalyzed Arylene Cyclization

Abstract

Novel Hg(OTf) 2-catalyzed arylene cyclization was achieved with highly efficient catalytic turnover (up to 200 times). The reaction takes place via protonation of allylic hydroxyl group by in situ formed TfOH of an organomercuric intermediate to generate a cationic species. Subsequent smooth demercuration regenerates the catalyst.

Enantioselective Gold‐Catalyzed Allylic Alkylation of Indoles with Alcohols: An Efficient Route to Functionalized Tetrahydrocarbazoles

“…However, at present an analogous mechanistic pathway involving monometallic gold-activation and Brønsted acid assisted b-hydroxy elimination cannot be ruled out (Figure 3, right cycle). [27] Different to what commonly occurs in the gold-catalyzed hydroarylations of allenes, a final proton-deauration event is not operating here, and the Brønsted acid present in solution seems to act as a scavenger for the hydroxy groups. This proposal is supported by the fact that while in allene chemistry the addition of bases completely suppresses the catalytic cycle, [28] in our model reaction ((Z)-1 a, L10-(Au 2 Cl 2 )/AgOTf, RT) the use of noncoordinating 2,6-di-tertbutylpyridine (30 mol %) simply caused a drop in the reaction rate (25 % conv., 20 h) because of the formation of less acidic pyridium salt, with almost unvaried levels of stereoinduction (90 % ee).…”

Exploring the Reactivity of α‐Lithiated Aryl Benzyl Ethers: Inhibition of the [1,2]‐Wittig Rearrangement and the Mechanistic Proposal Revisited

“…[35] However, this catalyst proved unsuccesful for substrates possesing secondary hydroxyl groups such as 11d and 11j, which could be cyclized in low yield to the corresponding dihydrobenzofuran 12 as variable mixture of diastereoisomers employing Hg(OTf) 2 as catalyst (Scheme 8). [36] Interestingly, benzofuran derivative 12g was obtained as single diastereoisomer whose configuration was initially assigned to the trans isomer based on the comparison between the experimental and mPW1PW91/6-311+G(2d,p)(PCM,CH 2 Cl 2 ) 1 H NMR spectra for the two diastereomers. [37] In addition, the complete stereoselectivity was further supported by the computational characterization of the four diastereomeric cyclization transition states between 11g and 12g, finding that the transition state responsible for the formation of the trans isomer is about 1.86 kcal mol 1 lower in energy than the lowest energy TS leading to the cis product.…”

4.07 Electrophilic Cyclization

“…The reaction takes place via protonation of allylic hydroxyl group by in situ formed TfOH of an organomercuric intermediate to generate a cationic species (Scheme 169). 182 In 2007, Nishizawa and coworkers report that a 10:1 mixed reagent of Hg(OAc) 2 and Sc(OTf) 3 showed remarkable catalytic activity for the Friedel-Crafts-type cycloisomerization of 2-(4-pentynyl)furan (Scheme 170). 183 The actual reacting species is presumed to be Hg(OAc)(OTf), which is efficiently generated in situ by mixing the two reagents.…”