Samarium(III) Iodide Complex Catalyzed Regioselective Cleavage of Epoxides to Iodohydrins: Tandem Epoxide Opening-Iodocyclization

Abstract

A novel tandem iodocyclization has been achieved by the regioselective ring-opening of epoxide and by the following intramolecular 1,4-cycloaddition of α,β-unsaturated ester with catalytic amount of SmI₂ and I₂ (1.2-2.5 equivalent) under mild and neutral reaction conditions.

Key words

samarium - tandem reactions - ring opening - cyclizations - regioselectivity

References

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10

Sm(III) iodide and SmI₂(t-BuO) were tested for the reaction with 1e. However, their catalytic amount (10 mol%) did not act as the catalysts at 25 °C: product 2e could not be obtained, but starting material was recovered.

11

2e: ¹H NMR (CDCl₃, 400 MHz) δ 4.18 (b, 1 H), 3.98 (m, 1 H), 3.71 (m, 1 H), 3.47 (m, 1 H), 2.16 (m, 1 H), 1.89 (m, 1 H), 1.65 (m, 1 H), 0.98 (t, 3 H); ¹³C NMR (CDCl₃) δ 84.5, 71.9, 65.5, 35.6, 21.7, 10.6; HREIMS [M⁺] Calcd. for C₆H₁₃IO₂. 243.9960, found 243.9954. 2f: ¹H NMR (CDCl₃, 400 MHz) δ 4.20 (m, 1 H), 3.88 (m, 2 H), 3.60 (m, 1 H), 2.10 (bs, 2 H, OH), 1.86 (m, 4 H), 1.07 (t, J = 7.2 Hz, 3 H); ¹³C NMR (CDCl₃) δ 74.7, 65.7, 42.6, 35.7, 28.6, 14.3; HREIMS [M⁺] Calcd for C₆H₁₃IO_2. 243.9960, found 243.9975.

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5a: ¹H NMR (CDCl₃, 400 MHz) δ 5.21 (d, J = 6.77 Hz, 1 H), 4.40 (m, 1 H), 4.32 (d, J = 6.73 Hz, 1 H), 4.20 (m, 2 H), 4.18 (m, 1 H), 3.92 (m, 1 H), 3.22 (m, 2 H), 1.27 (m, 3 H); ¹³C NMR (CDCl₃) δ 168.4, 104.3 (two), 77.2, 76.5, 71.2, 70.5, 62.1, 22.0, 21.9, 13.7, 5.4, 4.9; HREIMS [M⁺] Calcd for C₈H₁₂I₂O_4. 425.8825, found 425.8824.