5130
M. Terrazas et al. / Tetrahedron Letters 46 (2005) 5127–5130
J. L. Angew. Chem., Int. Ed. Engl. 1994, 33, 2454; (c) Ariza,
X. Ph.D. Thesis; Universitat de Barcelona, 1995; (d) Ariza,
X.; Bou, V.; Vilarrasa, J. J. Am. Chem. Soc. 1995, 117,
regarding the ring-opening step (attack on C2), is that al-
ready indicated. In general, this ring-opening step is quite
rapid, although the open intermediates are often contam-
inated by relatively significant percentages of desulfonyl-
ation by-products (by attack on the sulfur atom, or in
the case of 2h by attack on Cipso). Difficulties also appear
in the ring-closing step, since most intermediates of type
3 and 5* decompose on heating more rapidly than they
cyclise. The Tf group (see 2b), of which we had reason-
able expectations owing to its very strong EW character,
is useless, for both the N-alkylation reaction and 15N
labelling. Surprisingly, the Ns group (see 2f) affords the
best yields of 4 and 6*, since it is the case in which the
number and amount of by-products produced in both
steps are minimal. Thus, another advantage of Ns as
the activating or protecting group is now disclosed.
`
3665; (e) Ariza, X.; Farras, J.; Serra, C.; Vilarrasa, J.
J. Org. Chem. 1997, 62, 1547; (f) Ariza, X.; Vilarrasa, J.
J. Org. Chem. 2000, 65, 2827; (g) Terrazas, M.; Ariza, X.;
`
Farras, J.; Guisado-Yang, J. M.; Vilarrasa, J. J. Org. Chem.
2004, 69, 5473.
2. See references cited in the following reviews and papers: (a)
Kawashima, E.; Kamaike, K. Mini-Rev. Org. Chem. 2004,
1, 309; (b) Shallop, A. J.; Gaffney, B. L.; Jones, R. A. J.
Org. Chem. 2003, 68, 8657; (c) Wenter, P.; Pitsch, S. Helv.
Chim. Acta 2003, 86, 3955; (d) Desaulniers, J.-P.; Ksebati,
B.; Chow, C. S. Org. Lett. 2003, 5, 4093; (e) Lagoja, I. M.;
Herdewijn, P. Synthesis 2002, 301; (f) Milecki, J. J. Labelled
Compd. Radiopharm. 2002, 45, 307; (g) Gorchs, O.;
´
Hernandez, M.; Garriga, L.; Pedroso, E.; Grandas, A. J.;
`
Farras, J. Org. Lett. 2002, 4, 1827; (h) Dunger, A.;
Limbach, H.-H.; Weisz, K. J. Am. Chem. Soc. 2000, 122,
10109; (i) Matsuo, H.; Moriguchi, T.; Takagi, T.; Kusa-
kabe, T.; Buratowski, S.; Sekine, M.; Kyogoku, Y.;
Wagner, G. J. Am. Chem. Soc. 2000, 122, 2417.
Acknowledgements
3. (a) De Napoli, L.; Messere, A.; Montesarchio, D.; Piccialli,
G. J. Org. Chem. 1995, 60, 2251; (b) De Napoli, L.;
Messere, A.; Montesarchio, D.; Piccialli, G.; Varra, M. J.
Chem. Soc., Perkin Trans. 1 1997, 2079.
4. The tosyl derivative (2c) was known: (a) Shaw, E. J. Am.
Chem. Soc. 1959, 81, 6021 (prepared from triacetyl inosine
and NaH in DMF). The N1-mesitylenesulfonyl derivative
of 30,50-di-O-acetyl-20-deoxyinosine has been reported as
well; (b) Xu, Y.-Z.; Zheng, Q.; Swann, P. F. Tetrahedron
Lett. 1992, 33, 5837 (see Refs. 7 and 8 therein).
5. For the use of sulfonyl derivatives as protecting or
activating groups, see: (a) Greene, T. W.; Wuts, P. G. M.
Protective Groups in Organic Synthesis; Wiley: New
York, 1999; (b) Wuts, P. G. M.; Northuis, J. M. Tetrahe-
dron Lett. 1998, 39, 3889; (c) Nihei, K.; Kato, M. J.;
Yamane, T.; Palma, M. S.; Konno, K. Synlett 2001, 1167;
(d) Kan, T.; Fukuyama, T. Chem. Commun. 2004, 353.
6. (a) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91,
165; (b) SciFinder-based search.
We thank the Spanish MCyT (Madrid, BQU2000-0647)
and the DURSI of the Generalitat de Catalunya (Barce-
lona, 2001SGR 051) for financial support. A studentship
to M.T. (EU RDG, Brussels, FP6) is also acknowledged.
Supplementary data
1
Selection of H (400 MHz) and 13C (100.6 MHz) NMR
spectra, corresponding to compounds 2b, 2c, 2f, 2g and
2h, intermediate 3f, compound 4, intermediate 5f0* and
compound 6*. Supplementary data associated with this
article can be found, in the online version, at
References and notes
1. (a) Bou, V. Ph.D. Thesis; Universitat de Barcelona, 1992;
(b) Ariza, X.; Bou, V.; Vilarrasa, J.; Tereshko, V.; Campos,
7. On the other hand, on heating, without additives, only 3b
cyclised to 4, even though in poor yield (30%).