Asymmetric [2+2+1] cyclopentannulation of olefins. Ring expansion of 2-N-methyl-N-tosyl-cyclobutanone
(2002) Tetrahedron — Vol. 58, n° 35, p. 6991-7000 (2002)
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- alpha-N-Methyl-N-tosyl cyclobutanones 2 which had been previously prepared in good yields and high enantiomeric excesses from olefins and chiral keteniminium salts have been converted into the corresponding oxiranes 3 by reaction with dimethylsulfonium methylid. The stereochemistry of this reaction was found to be dependent on several factors which have been analyzed. Treatment of these oxiranes with a stoichiometric amount of lithium iodide in refluxing tetrahydrofuran gave excellent yields of monocyclic or fused cyclopentenones 4 resulting from a P-elimination of N-methyl-N-tosylamide from a primarily formed cyclopentanone. The ring-expansion was totally selective but for oxiranes attached to a bicyclo[4.2.0]octanone system. In all cases, the enantiomeric purities of the starting cyclobutanones were preserved throughout the sequence which thus represents a useful [2+2+1] strategy for the cyclopentannulation of olefins. (C) 2002 Elsevier Science Ltd. All rights reserved.
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Mahuteau-Betzer, F., & Ghosez, L. (2002). Asymmetric [2+2+1] cyclopentannulation of olefins. Ring expansion of 2-N-methyl-N-tosyl-cyclobutanone. Tetrahedron, 58(35), 6991-7000. https://doi.org/10.1016/S0040-4020(02)00694-4 (Original work published 2002)