Studies on the factors controlling the stereoselectivity in electrophilic iodocyclization of alkylidenecyclopropyl ketones |
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Authors: | Jie Chen |
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Institution: | State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, PR China |
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Abstract: | An efficient electrophilic iodocyclization of alkylidenecyclopropyl ketones with N-iodosuccinimide (NIS) or I2 in aqueous CH3CN affording 3-oxabicyclo3.1.0]hexan-2-ols is described. NIS is a better electrophilic iodocyclization reagent than I2. Four chiral centers were formed within one step. The stereochemistry was established by the X-ray diffraction studies of compounds 2e-2h, 2n, and 2c. It is quite interesting to observe that the substituent of the cyclopropane ring plays an important role in determining the relative stereochemistry at the 4-position: with R2 being an acyl or ester group a mixture of (1S∗,2R∗,4S∗,5R∗)-2 (major) and (1R∗,2R∗,4R∗,5R∗)-2 (minor) was formed with moderate selectivity while the reaction of the substrates with R2 being sulfonyl and p-methylphenylsulfonyl or R1 being phenyl afforded (1R∗,2R∗,4S∗,5S∗)-2 or (1S∗,2R∗,4S∗,5R∗)-2f as the only product. The reaction is general for a range of different substrates to afford the products in moderate to high yields. |
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Keywords: | Iodocyclization Alkylidenecyclopropyl ketones Stereoselectivity 3-Oxabicyclo[3 1 0]hexan-2-ols |
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