Regiocontrol of radical cyclization by Lewis acids. Efficient synthesis of optically active functionalized cyclopentanes and cyclohexanes.
[figure: see text] Treatment of alpha-alkylidenelactones 3a-d with Bu3SnH and a catalytic amount of Et3B effected a 5-exo radical cyclization preferentially to provide the corresponding 1 and 2 in a ratio of 70:30 to 100:0. Meanwhile, the reaction of 3a and 3b in the presence of Et2AlCl proceeded via a 6-endo cyclization pathway predominantly to afford 2a and 2b with 90% and 92% regioselectivity, respectively.
Kim
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Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
Okamoto
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S
Sato
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F