Ring-Opening Hydroarylation of Monosubstituted Cyclopropanes Enabled by Hexafluoroisopropanol

Abstract

<div><p>Ring-opening hydroarylation of cyclopropanes is typically limited to substrates bearing a donor-acceptor motif. Here, the transformation is achieved for monosubstituted cyclopropanes by using catalytic Brønsted acid in hexafluoroisopropanol (HFIP) solvent, constituting a rare example where such cyclopropanes engage in intermolecular C–C bond formation. Branched products are obtained when electron-rich arylcyclopropanes react with a broad scope of arene nucleophiles in accord with a simple S<sub>N</sub>1-type ring-opening mechanism. In constrast, linear products are obtained when cyclopropylketones react with electron-rich arene nucleophiles. In the latter case, mechanistic experiments and DFT-calculations support a homo-conjugate addition pathway.</p></div>

Hydroarylation of Alkenes by Protonation/Friedel–Crafts Trapping: HFIP-Mediated Access to Per-aryl Quaternary Stereocenters

“…Following the general procedure 2 for organocatalytic hydroarylation of 4-methyl-1,2-dihydronaphthalene. Isolated as a clear oil (25.0 mg, 0.0991 mmol, 99%): 1 H NMR (400 MHz, chloroform-d) δ 7.12−6.99 (m, 6H), 6.78 (d, J = 8.9 Hz), 3.77 (s, 3H), 2.83 (t, J = 6.5 Hz, 2H), 2.02 (ddd, J = 13.2, 8.2, 3.2 Hz, 1H), 1.86 (ddd, J = 13.2, 9.1, 3.0 Hz, 1H), 1.81−1.72 (m, 1H), 1.70 (s, 3H), 1.69−1.61 (m, 1H); 13 1-(4-Methoxyphenyl)-1-methyl-2,3-dihydro-1H-indene (5). Following the general procedure 2 for organocatalytic hydroarylation of 3-methyl-1H-indene.…”

Electrophilic fluorosulfoxonium cations as hidden Brønsted acid catalysts in (n + 2) annulations of strained cycloalkanes

“…The latter was indeed chosen for its potency as a strong Brønsted acid and as an attempt of continuity with the work of Wang et al and Moran et al on reactions of D-A cyclopropane derivatives mediated by TfOH. 50,51 Surprisingly, the (3+2) cyclisation of D-A cyclopropanes with carbonyl derivatives under Brønsted acid catalysis was not reported. Accordingly, we assessed TfOH in these reactions and applied the same conditions as for the (3+2) cyclisation mediated by Cat.1 (Figure 6).…”