1722
J. M. Barks et al.
LETTER
(11) Barks, J. M.; Gilbert, B. C.; Parsons, A. F.; Upeandran, B.
Tetrahedron Lett. 2000, 41, 6249.
(12) Barks, J. M.; Gilbert, B. C.; Parsons, A. F.; Upeandran, B.
Tetrahedron Lett. 2001, 42, 3137.
Acknowledgement
We thank the EPSRC and Zeneca/Syngenta for funding a CASE
award.
(13) For related intramolecular radical reactions mediated by
phosphinic acid derivatives see: (a) Yorimitsu, H.;
Shinokubo, H.; Oshima, K. Bull. Chem. Soc. Jpn. 2001, 74,
225. (b) Kita, Y.; Nambu, H.; Ramesh, N. G.; Anilkumar,
G.; Matsugi, M. Org. Lett. 2001, 3, 1157. (c) Graham, S.
R.; Murphy, J. A.; Kennedy, A. R. J. Chem. Soc., Perkin
Trans. 1 1999, 3071.
References
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(14) The rate of hydrogen-atom abstraction from diethyl
phosphite by a primary radical has been shown to be
1.2 105 dm3 mol–1 s–1 at 130 °C, see: Chatgilialoglu, C.;
Timokhin, V. I.; Ballestri, M. J. Org. Chem. 1998, 63, 1327.
(15) General experimental procedure. A stirred solution of
benzoyl peroxide (0.3 equiv.), carbon tetrachloride (4
equiv.), diethyl phosphite (10–20 equiv.) or di-tert-butyl
phosphite (5 equiv.), and the alkene (2–2.5 mmol, 1 equiv.)
in degassed cyclohexane (20 cm3) was heated at reflux under
a nitrogen atmosphere. After 12–15 h, the solvent was
evaporated and saturated aqueous potassium carbonate
(20 cm3) was added. The mixture was then extracted with
diethyl ether, washed with brine, dried (MgSO4) and
evaporated. Purification by column chromatography (silica)
afforded tri- and tetra-chlorinated adducts as colourless oils.
(16) (a) Piettre, S. R. Tetrahedron Lett. 1996, 37, 2233.
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(2) For a related approach using the trichloromethyl anion see:
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Tetrahedron Lett. 2000, 41, 6071. (b) Simal, F.; Sebille, S.;
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Teixidor, F.; Viñas, C. Tetrahedron Lett. 2000, 41, 5347.
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(17) Heating 1-octanol (1 equiv.) with diethyl phosphite (1.5
equiv.) in cyclohexane for 20 h also led to transesterification
and the formation of ethyl octyl phosphite in 60% yield
(after column chromatography).
(18) For related reactions see: (a) Gancarz, R.; Gancarz, I.
Phosphorus Sulfur 1993, 77, 306. (b) Froneman, M.;
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(19) The reaction of CCl4 and di-tert-butyl phosphite with allyl
alcohol was less efficient and the tri- and tetrachloro-
alcohols were formed in 18% and 9% yield, respectively.
This may be explained by competitive hydrogen atom
abstraction at the allylic position.
(9) All new compounds exhibited satisfactory spectral and
analytical (high resolution mass) data.
(10) We would like to thank a referee who pointed out that the
trichloromethyl radical could prefer to abstract a hydrogen
atom from 1,4-cyclohexadiene (and related compounds)
rather than add to the alkene double bond. This is certainly
possible although we expected competitive alkene addition
because reaction of 1,4-cyclohexadiene with BrCCl3 (in
THF in the absence of an alkene) produced halogenated
products (albeit in 15% yield) derived from addition of the
trichloromethyl radical to a double bond of the diene.
Synlett 2001, No. 11, 1719–1722 ISSN 0936-5214 © Thieme Stuttgart · New York