Asymmetric Iodocyclization of γ-Hydroxyalkenes

Abstract

Enantioselective intramolecular iodoetherification of disubstituted γ-hydroxyalkenes has been intended using NIS in the presence of 0.2 equivalents of (R)-Binol-Ti(IV) complex to procure the corresponding tetrahydrofurans in up to 65% ee.

Key words

reagent-controlled - iodocyclization - γ-hydroxyalkenes - (R)-Binol-Ti(IV) complex - N-iodosuccinimide

References

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10

General Procedure for the Asymmetric Iodocyclization. To a mixture of (R)-Binol (17 mg, 0.06 mmol) and 4Å molecular sieve (57 mg) in t-butyl methyl ether (3.5 mL) was added Ti(Oi-Pr)₄ (17 mg, 0.06 mmol) in t-butyl methyl ether (0.7 mL) at r.t., and the resulting mixture was stirred at that temperature for 1.5 h. After cooling the generated (R)-Binol-Ti(IV) complex to 0 °C, the substrate 2 (57 mg, 0.3 mmol) in t-butyl methyl ether (1.5 mL) and N-iodo-succinimide (81 mg, 0.36 mmol) were added in sequence. The iodocyclization was allowed to proceed at 0 °C for 3 h, and then quenched with 10% aq Na₂S₂O₃ (3 mL). The reaction mixture was extracted with Et₂O (3 × 5 mL), and subsequently the organic layer was filtered through celite. Evaporation of the volatile materials in vacuo followed by silica gel column chromatography (Et₂O-hexane = 1:15) yielded tetrahydrofuran 3 (89 mg, 93%).