7758
A. Fern a´ ndez-Mateos et al. / Tetrahedron Letters 47 (2006) 7755–7758
Scheme 10.
3
. The seminal work for radical cyclizations onto carbonyls
induced by Cp
TiCl: (a) Fern a´ ndez-Mateos, A.; Mart ´ı n de
2
la Nava, E.; Pascual Coca, G.; Ramos Silvo, A.; Rubio
Gonz a´ lez, R. Org. Lett. 1999, 1, 607; In this work a b-
hydrogen elimination with titanocene chloride was also
2
reported for the first time. The seminal work on Cp TiCl
Scheme 11.
chemistry: (b) RajanBabu, T. V.; Nugent, W. A. J. Am.
Chem. Soc. 1994, 116, 986; For outstanding revisions on
2
the chemistry of Cp TiCl see: (c) Gans a¨ uer, A.; Bluhm, H.
Chem. Rev. 2000, 100, 2771–2788; (d) Gans a¨ uer, A.;
Lauterbach, T.; Narayan, S. Angew. Chem., Int. Ed. 2003,
tion of epoxy formate to titanocene chloride, only 14b
(
52%) and 14c (19%) were obtained.
4
2, 5556; (e) Barrero, A. F.; Quilez del Moral, J. F.;
S a´ nchez, E. M.; Arteaga, J. F. Eur. J. Org. Chem. 2006,
627; (f) Cuerva, J. M.; Justicia, J.; Oller-L o´ pez, J. L.;
Bazdi, B.; Oltra, J. E. Mini-Rev. Org. Chem. 2006, 3, 23.
The analogous epoxyacetate 15 by reaction with Ti(III)
only gave a mixture of hydroxyacetate diastereomers
1
1
5ab (92%, Scheme 11) from the 5-exo cyclization onto
´
´
´
4
5
. Fernandez-Mateos, A.; Mateos Buron, L.; Martın de la
Nava, E. M.; Rabanedo Clemente, R.; Rubio Gonz a´ lez,
R.; Sanz Gonz a´ lez, F. Synlett 2004, 2553.
the C@C double bond.
. In the literature we have found only two examples: an old
radical cyclization onto ester (a) Nikishin, G. I.; Starostin,
E. K.; Golovin, B. A.; Kessevich, A. V.; Iguatenko, A. V.
Izvest. Akad. Nauk. SSSR Ser. Khim. 1971, 1842, and a
new one onto lactone; (b) Ruano, G.; Martia n˜ ez, J.;
Grande, M.; Anaya, J. J. Org. Chem. 2003, 68, 2024.
. (a) The new compounds were prepared by standard
procedures from readily available starting materials. The
syntheses will be reported elsewhere; (b) The structures of
all new compounds were supported by spectral data. See
Supplementary data.
Acknowledgments
Financial support for this work from the Ministerio de
Ciencia
Tecnolog ´ı a of Spain (PPQ2002-00290)
CTQ2005-05026/BQU) and the Junta de Castilla y
y
(
6
7
Le o´ n (SA079A06) is gratefully acknowledged. We also
thank the M.C.y T. of Spain and the Universidad de
Salamanca for the fellowships to R.R.C. and P.H.T.
. Daasbjerg, K.; Svith, H.; Grimme, S.; Gerenkamp, M.;
Muck-Lichtenfeld, C.; Gans a¨ uer, A.; Barchuk, A.; Keller,
F. Angew. Chem., Int. Ed. 2006, 45, 2041.
Supplementary data
8
9
. Fern a´ ndez-Mateos, A.; L o´ pez Barba, A. M. J. Org. Chem.
1
995, 60, 3580.
. For a discussion about the reduction of tertiary radicals
with Ti(III) see: Barrero, A. F.; Oltra, J. E.; Cuerva, J. M.;
Rosales, A. J. Org. Chem. 2002, 67, 2566.
1
1
0. Baumberger, F.; Vasella, A. Helv. Chim. Acta 1983, 66,
References and notes
. (a) Kim, S. Adv. Synth. Catal. 2004, 346, 19, and
references cited therein; (b) Curran, D. P. In Comprehen-
sive Organic Synthesis; Trost, B. M., Flemming, I., Eds.;
Pergamon Press: London, 1991; Vol. IV, p 779; (c) Giese,
B.; Kopping, B.; G o¨ bel, T.; Dickhaut, J.; Thoma, G.;
Kulicke, K. J.; Trach, F. Organic Reactions 1996, 48, 308.
. (a) Beckwith, A. L. S.; Raner, K. D. J. Org. Chem. 1992,
2210.
1
3
1. The structures of epoxides 12 and 13 were based on
C
1
NMR: Davis, R.; Kluge, A. F.; Maddox, M. L.; Spara-
cino, M. L. J. Org. Chem. 1983, 48, 255, and confirmed by
reduction of the separated diastereomeric epoxides to
diols: Adams, J.; Hoffman, Jr.; Trost, B. M. J. Org. Chem.
1970, 35, 1600.
12. Only two diastereomers 12a and 12b were obtained in a 6:4
ratio, respectively. Their structures were confirmed by
oxidation to the corresponding ketolactones. The same
was done for hemiketals: 3b, 4a, 4b, and 5a. See
Supplementary data.
2
57, 4954; (b) Walton, R.; Fraser-Reid, B. J. Am. Chem.
Soc. 1991, 113, 5791; (c) Devin, P.; Fensterbank, L.;
Malacria, M. Tetrahedron Lett. 1999, 40, 5511.