New Elements in the Reactivity of α-Cyclopropyl Vinyl Radicals

Abstract

The reactivity of the α-cyclopropyl vinyl radical has been examined through the use of propargylic bromomethyldime­thylsilyl ethers bearing a cyclopropyl group on the acetylenic moiety. With unsubstituted precursors, allenes can be obtained. With appropriate trapping possibilities (5-exo cyclization or hydrogen transfer), the cyclopropyl moiety on the vinyl radical is retained.

Key words

vinyl radicals - cyclizations - ring opening - hydrogen transfer - cyclopropanes

References

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• 14b

  Mouriès, V.; Delouvrié, B.; Lacôte, E.; Fensterbank, L.; Malacria, M. Eur. J. Org. Chem. 2002, in press.

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• 16b

  Spectral data for 13. IR(neat): 3350, 3080, 2950, 1640, 1250 cm^-1; ¹H NMR (400 MHz, CDCl₃) δ 4.40 (m, 1 H, CH-OH), 2.31 (m, 2 H, CH ₂ cyclopentenol + CHCH₃), 1.76 (d, J = 13.8 Hz, 1 H, CH ₂Si), 1.64 (d, J = 13.8 Hz, 1 H, CH ₂Si), 1.34 (m, 1 H, CH cyclopropane), 1.26 (m, 1 H, CH ₂ cyclopentenol), 1.11 (d, J = 6.6 Hz, 3 H, CH ₃ ), 0.70 (m, 2 H, cyclopropane), 0.55 (m, 1 H, cyclopropane), 0.41 (m, 1 H, cyclopropane), 0.04 [9 H, Si(CH ₃)₃]; ¹³C NMR (100 MHz, CDCl₃) δ 141.2 (C, C=C), 137.1 (C, C=C), 79.9 (CH, CH-OH), 41.9 (CH₂, cyclopentenol), 38.6 (CH, cyclopentenol), 23.0 (CH₃), 16.4 (CH₂, CH₂Si), 9.7 (CH, cyclopropane), 5.8 (CH₂, cyclopropane), 5.2 (CH₂, cyclopropane), -0.4 [3 CH₃, Si(CH₃)₃]. Anal. Calcd. for C₁₃H₂₄OSi: C, 69.58; H, 10.78. Found: C, 69.55; H, 10.89.

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• 17c

  Although the Beckwith system cannot directly be compared to the system studied herein (different substitution pattern), this data could suggest an intrinsic faster cyclization of the vinyl radical, thus contributing significantly to the observed effect.

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13

Spectroscopic data for 10. IR(neat): 2960, 1960, 1750, 1450, 1370, 1270 cm^-1; ¹H NMR (200 MHz, CDCl₃) δ 5.21 (m, 1 H, vinyl), 4.48 (t, J = 2.0 Hz, 2 H, CH ₂ O), 3.75 (s, 3 H, CO₂CH ₃ ), 1.97 (quint, J = 7.4 Hz, 2 H, CH ₂ CH₃), 1.32 (m_AB, 2 H, CH ₂ Si), 0.97 (t, J = 7.4 Hz, 3 H, CH ₃ ), 0.02 (s, 9 H, Si(CH ₃ )₃); ¹³C NMR (50 MHz, CDCl₃) δ 201.8 (C, C=C=CH), 155.8 (C, C=O), 97.4 (C, C=C=CH), 94.8 (CH, C=C=CH), 70.1 (CH₂, CH₂O), 54.8 (CH₃, CO₂ CH₃), 22.5 (CH₂, CH₂CH₃), 18.2 (CH₂, CH₂Si), 13.6 (CH₃), -1.3 (3 CH₃, Si(CH₃)₃). Anal. Calcd. for C₁₂H₂₂O₃Si: C, 59.46; H, 9.15. Found: C, 59.34; H, 9.35.