Au(I)-Catalyzed Cyclization of tert-Butyl Carbonates Derived from ­Homopropargyl Alcohols: A Catalytic Alternative to Cyclic Enol Carbonates

Abstract

Au(I)-complexes catalyze cyclization of tert-butyl ­carbonates derived from a variety of homopropargyl alcohols. This procedure offers a catalytic alternative to stoichiometric Lewis ­acids for the preparation of a range of enol carbonates.

Key words

gold catalysis - tert-butyl carbonate - homopropargyl ­alcohol - enol carbonate - ligand

References and Notes

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7

The β-hydroxyketone 3a is formed during the reaction, not during the subsequent workup. For example, upon a long-term storage of 2a, there was no change in the spectral integrity or in its TLC profile.

10

Representative Procedure for the Cyclization of 1d into 2d.
To a solution of 1d (100 mg, 0.384 mmol) in 1,2-dichloro-ethane (2 mL) at 0 °C, was added Au(PAr₃)Cl (Ar = C₆F₅) (14.3 mg, 19.2 µmol), followed by AgSbF₆ (6.6 mg, 19.2 µmol). Upon addition of AgSbF₆, the color of the reaction mixture immediately turned to orange. The reaction mixture was kept at 0 °C for 15 h, then was slowly allowed to warm to r.t. over 5 h. After the reaction was judged to be complete by TLC, the crude mixture was concentrated to ca. 0.5 mL and was loaded on silica gel column and was eluted with EtOAc-hexane (1:4) to obtain 62.8 mg (80%) of 2d as pale yellow oil, along with 5.7 mg (8%) of hydrolyzed by-product, 3d.
For compound 2a see ref. 2.
Compound 2b: IR: 1777 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.40 (d, J = 7.9 Hz, 2 H), 7.31 (d, J = 7.8 Hz, 2 H), 5.42 (dd, J = 3.3, 10.7 Hz, 1 H), 4.87 (dd, J = 1.5, 2.2 Hz, 1 H), 4.44 (app t, J = 1.8 Hz, 1 H), 2.93 (dd, J = 3.3, 15.4 Hz, 1 H), 2.76 (tdd, J = 1.5, 10.6, 15.4 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 150.8, 146.7, 135.9, 135.6, 129.9, 127.8, 95.8, 78.7, 33.8. MS (EI): m/z = 181 [M - CO₂ + H].
Compound 2c: IR: 1779 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.33 (t, J = 7.7 Hz, 1 H), 6.94-6.88 (m, 3 H), 5.41 (dd, J = 3.3, 10.6 Hz, 1 H), 4.86 (app t, J = 1.8 Hz, 1 H), 4.42 (app t, J = 1.9 Hz, 1 H), 3.81 (s, 3 H), 2.93 (dd, J = 3.3, 15.4 Hz, 1 H), 2.79 (tdd, J = 1.9, 10.7, 15.4 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 160.0, 150.4, 146.3, 137.9, 130.0, 117.8, 114.7, 111.2, 94.8, 78.6, 55.3, 33.2.
Compound 2d: IR: 1780 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.35-7.25 (m, 1 H), 7.24-7.12 (m, 3 H), 5.40 (dd, J = 3.3, 10.3 Hz, 1 H), 4.85 (app t, J = 2.2 Hz, 1 H), 4.42 (app t, J = 1.8 Hz, 1 H), 2.92 (dd, J = 3.2, 15.0 Hz, 1 H), 2.79 (tdd, J = 1.4, 10.6, 15.4 Hz, 1 H), 2.39 (s, 3 H). ¹³C NMR 100 MHz, CDCl₃): δ = 151.2, 147.1, 139.5, 137.1, 130.7, 129.5, 127.0, 123.4, 95.4, 79.5, 33.9, 22.1.
Compound 2e: IR: 1772 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 4.77 (app t, J = 1.8 Hz, 1 H), 4.36 (app t, J = 1.4 Hz, 1 H), 4.15 (ddd, J = 2.3, 6.9, 10.2 Hz, 1 H), 2.65 (dd, J = 2.9, 15.0 Hz, 1 H), 2.50 (tdd, J = 1.5, 10.3, 15.0 Hz, 1 H), 2.00 (m, 1 H), 1.85-1.07 (m, 10 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.7, 147.4, 94.9, 82.6, 41.9, 29.1, 28.6, 28.4, 26.7, 26.3, 26.1.
Compound 2f: IR: 1772 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 4.79 (t, J = 1.5 Hz, 1 H), 4.44 (m, 1 H), 4.37 (t, J = 1.5 Hz, 1 H), 2.70 (dd, J = 3.3, 15.4 Hz, 1 H), 2.46 (tdd, J = 1.5, 9.5, 15.0 Hz, 1 H), 1.77 (m, 1 H), 1.75-1.38 (m, 3 H), 0.97 (t, J = 7.3 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.4, 147.3, 95.0, 78.3, 37.0, 31.5, 18.5, 14.3.
Compound 2g: IR: 1775 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 4.78 (t, J = 1.9 Hz, 1 H), 4.37 (t, J = 1.9 Hz, 1 H), 4.13 (ddd, J = 2.9, 6.6, 10.6 Hz, 1 H), 2.66 (dd, J = 3.0, 15.1 Hz, 1 H), 2.48 (tdd, J = 1.5, 10.6, 15.4 Hz, 1 H), 1.93 (m, 1 H), 1.05 (d, J = 7.0 Hz, 3 H), 0.99 (d, J = 7.0 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.6, 147.4, 94.9, 83.2, 32.5, 29.0, 18.2, 18.1.
Compound 2h: IR: 1772 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 4.77 (dd, J = 0.7, 2.6 Hz, 1 H), 4.39 (dd, J = 1.4, 2.6 Hz, 1 H), 3.90 (dd, J = 4.4, 7.3 Hz, 1 H), 2.68 (m, 1 H), 1.92-1.52 (m, 7 H), 1.21 (d, J = 6.9 Hz, 3 H), 1.45-1.10 (m, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 156.7, 147.3, 93.7, 87.2, 39.8, 32.0, 29.8, 26.6, 26.3, 14.5.
Compound 2i: IR: 1773 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 4.80 (dd, J = 1.1, 2.6 Hz, 1 H), 4.40 (dd, J = 1.5, 2.6 Hz, 1 H), 4.10 (dt, J = 4.0, 8.1 Hz, 1 H), 2.52 (m, 1 H), 1.75-1.47 (m, 3 H), 1.47-1.20 (m, 9 H), 1.23 (d, J = 7.0 Hz, 3 H), 0.88 (t, J = 7.0 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 156.6, 147.1, 93.8, 83.3, 34.7, 33.6, 32.4, 29.9, 29.7, 24.8, 23.3, 14.8, 14.3.