Grubbs Catalyst Promoted Oxacycloisomerization: An Easy Route to Bicyclic Dihydrofurans and Tricyclic Acetals

Abstract

Oxacycloisomerization of 1-hydroxy-2-propargyl cyclic derivatives was catalyzed by the first-generation Grubbs catalyst (Grubbs I) and led to good yields of bicyclic dihydrofurans. Tri­cyclic acetals were also obtained from cyclic alkyne diols using the same experimental procedure.

Key words

oxacycloisomerization - Grubbs I catalyst - 1-hydroxy-2-propargyl cyclic derivatives - bicyclic dihydrofuran - tricyclic acetals

References and Notes

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15

General Procedure for the Preparation of Bicyclic Dihydrofurans 7-9
Grubbs catalyst (5-10 mol%) was added to a solution of
1-hydroxy-2-propargyl cyclic intermediates (0.39 mmol) in anhyd toluene (4 mL) under an argon atmosphere. The mix-ture was stirred for 2 h at 80 ˚C. The solvent was removed under reduced pressure and compounds 7-9 were purified by column chromatography on silica gel (gradient: PE-Et₂O).

16

Data of Selected Compounds
Compound 7c: ^¹H NMR (300 MHz, CDCl₃): δ = 1.64-1.72 (4 H, m), 1.77 (3 H, s), 1.80-1.87 (2 H, m), 3.56 (3 H, s), 4.38-4.41 (1 H, m), 5.01 (1 H, dd, J = 1.4, 10.6 Hz), 5.22 (1 H, dd, J = 1.4, 17.2 Hz), 5.76 (1 H, dd, J = 10.6, 17.2 Hz) ppm. ^¹³C NMR (75 MHz, CDCl₃): δ = 13.2, 23.9, 38.7, 40.0, 51.7, 68.5, 98.4, 98.6, 113.9, 137.2, 155.8, 174.5 ppm.
Compound 7e: ^¹H NMR (300 MHz, CDCl₃): δ = 1.50-1.75 (5 H, m), 1.78 (3 H, s), 1.81 (1 H, dd, J = 5.5, 10 Hz), 2.04 (1 H, d, J = 7.2 Hz), 2.10 (1 H, dd, J = 6.0, 10.2 Hz), 2.18 (1 H, dd, J = 7.4, 14.3 Hz), 2.28 (1 H, dd, J = 6.0, 14 Hz), 3.68 (3 H, s), 4.44 (1 H, s), 4.90 (1 H, dd, J = 1.3, 10.2 Hz), 4.97 (1 H, dd, J = 1.6, 17.1 Hz), 5.78 (1 H, ddt, J = 6.6, 10.0, 17.1 Hz) ppm. ^¹³C NMR (75 MHz, CDCl₃): δ = 13.7, 24.1, 29.6, 35.4, 39.4, 39.9, 51.9, 66.6, 98.8, 99.8, 114.2, 138.7, 155.8, 175.5 ppm. IR: 1730, 1641, 1261 cm^-¹. MS (EI, 70): m/z (%) = 218(24) [M⁺ - H₂O], 191(76), 190(10), 175(10), 173(18), 166(24), 163(10), 149(21), 148(15), 147(14), 145(10), 138(14), 136(12), 135(20), 134(17), 133(100), 132(12), 131(23), 121(18), 119(10), 108(14), 107(18), 105(23), 95(15), 93(21), 91(71), 81(10), 79(28), 77(22), 67(19), 65(13), 55(16), 43(35), 41(16).
Compound 8c: ^¹H NMR (300 MHz, CDCl₃): δ = 1.25 (3 H, t, J = 7.17 Hz), 1.46-1.61 (6 H, m), 1.72-1.79 (2 H, m), 1.90 (1 H, dd, J = 3.8, 12.9 Hz), 2.26 (1 H, d, J = 15.7 Hz), 2.98 (1 H, d, J = 15.5 Hz), 4.13 (2 H, q, J = 7.2 Hz), 4.29-4.32 (1 H, m), 5.07 (1 H, dd, J = 1.3, 10.7 Hz), 5.30 (1 H, dd, J = 1.5, 17.0 Hz), 5.77 (1 H, dd, J = 10.7, 17.0 Hz) ppm. ^¹³C NMR (75 MHz, CDCl₃): δ = 14.1, 19.1, 21.2, 31.5, 31.7, 39.1, 51.3, 60.6, 81.5, 101.8, 114.8, 139.2, 159.7, 172.7 ppm. MS (EI, 70): m/z (%) = 236(11) [M⁺], 133(38), 134(35), 135(35), 136(12), 144(16), 145(36), 147(44), 148(14), 151(11), 161(27), 162(81), 163(100), 164(16), 91(90), 92(22), 93(32), 94(13), 95(30), 97(14), 104(11), 105(38), 106(22), 107(36), 108(11), 111(17), 117(20), 119(39), 120(34), 121(34), 123(17), 50(13), 51(18), 53(19), 55(82), 65(40), 67(42), 69(13), 70(16), 77(55), 78(13), 79(63), 81(14), 83(21).