Synlett 2007(7): 1130-1132  
DOI: 10.1055/s-2007-973907
LETTER
© Georg Thieme Verlag Stuttgart · New York

Iodine-Atom-Transfer-Type Carbocyclization of 2-(2-Propynyloxy)ethyl Iodides Involving a Lithium Alkylidene Carbenoid Intermediate

Toshiro Harada*, Chie Kitano, Kenta Mizunashi
Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
Fax: +81(75)7247580; e-Mail: harada@chem.kit.ac.jp;
Further Information

Publication History

Received 26 January 2007
Publication Date:
13 April 2007 (online)

Abstract

In the presence of 1-hexynyllithium, 2-(2-propynyl­oxy)ethyl iodides undergo carbocyclization with 1-iodo-1-hexyne to afford 3-(diiodomethylene)tetrahydrofurans in an atom-economical manner with incorporation of the two iodine atoms from the substrates and the reagent.

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Enyne 7 might be formed by the addition of 1-hexynyl-lithium to an alkylidene carbenoid intermediate4a followed by iodination of the resulting alkenyllithium.

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Representative Procedure for Carbocyclization (Table 2, Entry 4)
To a solution of 1-iodo-1-hexyne (0.12 mL, 0.75 mmol) in THF (1 mL) under argon atmosphere at 0 °C was added n-BuLi (1.6 M solution in hexane, 0.13 mL, 0.20 mmol). The resulting solution was stirred at 0 °C for 30 min. To the resulting solution of 1-hexynyllithium (0.2 mmol) and 1-iodo-1-hexyne (0.55 mmol) in THF was added iodoalkyne 5d (0.141 g, 0.50 mmol). The resulting solution was stirred at 40 °C for 1.5 h. The mixture was poured into H2O and extracted twice with EtOAc. The combined organic layers were dried (Na2SO4) and concentrated in vacuo. The residue was purified by flash chromatography (SiO2, 7% EtOAc in hexane) to give 0.165 g (81% yield) of 2d: 1H NMR (500 MHz, C6D6): δ = 1.11 (3 H, t, J = 7.0 Hz), 1.54 (3 H, s), 1.71 (3 H, s), 2.62 (1 H, dd, J = 5.5, 17.4 Hz), 2.88 (1 H, d, J = 17.4 Hz), 3.24 (1 H, m), 3.75 (1 H, m), 4.76 (1 H, d, J = 5.4 Hz). 13C NMR (125.8 MHz, C6D6): δ = -2.6, 15.2, 26.7, 27.0, 52.5, 62.4, 85.2, 99.0, 161.3. Anal. Calcd for C9H14O2I2: C, 26.49; H, 3.46. Found: C, 26.53; H, 3.59.