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High Regio-, Chemo-, and Stereoselectivity via Low-Temperature 4 + 3 Cycloadditions. Convergent Synthesis of Multifunctionalized Vinylmetals (M = Si, Sn) and S-Vinyl Benzenecarbothioates

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journal contribution
posted on 10.03.2000, 00:00 by Hartmut Beck, Christian B. W. Stark, H. Martin R. Hoffmann
A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at −95 °C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.

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