994
M. Alajarín et al.
LETTER
(8) For a seminal paper in which the PRE was recognized see:
(a) Fischer, H. J. Am. Chem. Soc. 1986, 108, 3925. (b) For
the naming of the principle of PRE see: Daikh, B. E.; Finke,
R. G. J. Am. Chem. Soc. 1992, 114, 2938. (c) For an
excellent review on the PRE see: Fischer, H. Chem. Rev.
2001, 101, 3581. (d) For examples of PRE in organic
synthesis see: Studer, A. Angew. Chem. Int. Ed. 2000, 39,
1108. (e) Wetter, C.; Jantos, K.; Woithe, K.; Studer, A. Org.
Lett. 2003, 5, 2899. (f) Studer, A. Chem.–Eur. J. 2001, 7,
1159. (g) Leroi, C.; Fenet, B.; Couturier, J.-L.; Guerret, O.;
Ciufolini, M. A. Org. Lett. 2003, 5, 1079. (h) Allen, A. D.;
Fenwick, M. F.; Henry-Riyad, H.; Tidwell, T. T. J. Org.
Chem. 2001, 66, 5759. (i) Wetter, C.; Studer, A. Chem.
Commun. 2004, 174.
crude material was chromatographed on a silica gel column,
using hexanes/EtOAc (9:1) as eluent.
1,4-Benzoxazine 9f: Rf = 0.48; yield 27%; colorless prisms
(Et2O); mp 177–178 °C. IR (nujol): 2234, 1625, 1258, 1220,
1164, 1117, 1074, 1044, 964, 889, 827, 741, 707 cm–1. 1H
NMR (300 MHz, CDCl3): d = 1.23 (s, 3 H), 1.50 (s, 3 H),
3.39 (d, 1 H, J = 13.5 Hz), 4.28 (d, 1 H, J = 13.5 Hz), 6.79
(d, 1 H, J = 8.7 Hz), 7.11 (dd, 1 H, J = 8.7, 2.7 Hz), 7.41
(very broad s, 8 H), 7.61 (d, 1 H, J = 2.7 Hz), 7.91 (broad s,
2 H). 13C NMR (75 MHz, CDCl3): d = 25.3, 27.6, 37.3 (s),
63.6, 64.2 (s), 116.7, 127.2 (s), 127.4, 127.7 (s), 128.3,
128.5, 128.6, 128.9, 130.0, 131.1, 133.9 (s), 136.4 (s), 137.0
(s), 145.2 (s), 164.9 (s). MS: m/z (relative intensity) = 402 (3)
[M+ + 2], 400 (8) [M+], 332 (100). Anal. Calcd for
C25H21ClN2O: C, 74.90; H, 5.28; N, 6.99. Found: C, 74.77;
H, 5.21; N, 7.11.
(9) Boivin, J.; Fouquet, E.; Schiano, A.-M.; Zard, S. Z.
Tetrahedron 1994, 50, 1769.
(10) (a) Walkington, A. J.; Whiting, D. A. Tetrahedron Lett.
1989, 30, 4731. (b) Ahmad-Junan, S. A.; Walkington, A. J.;
Whiting, D. A. J. Chem. Soc., Perkin Trans. 1 1992, 2313.
(11) Gutenberger, G.; Steckhan, E.; Blechert, S. Angew. Chem.
Int. Ed. 1998, 37, 660.
1,4-Benzoxazine 10f: Rf = 0.36; yield 55%; colorless prisms
(Et2O); mp 143–144 °C. IR (nujol): 2233, 1624, 1600, 1579,
1494, 1299, 1261, 1236, 1198, 1128, 971, 870, 819, 763,
709, 668 cm–1. 1H NMR (300 MHz, CDCl3): d = 1.47 (s, 3
H), 1.51 (s, 3 H), 4.77 (d, 1 H, J = 11.7 Hz), 4.92 (d, 1 H,
J = 11.7 Hz), 6.82 (d, 1 H, J = 8.7 Hz), 6.99 (dd, 1 H, J = 8.7,
2.4 Hz), 7.08–7.11 (m, 2 H), 7.15 (d, 1 H, J = 2.4 Hz), 7.16–
7.19 (m, 2 H), 7.28–7.35 (m, 6 H). 13C NMR (75 MHz,
CDCl3): d = 27.8, 28.9, 56.8 (s), 65.2, 118.3, 121.8 (s),
123.4, 124.7, 125.1 (s), 128.1, 128.2, 128.4, 128.5, 129.8,
130.6, 132.4 (s), 139.5 (s), 140.2 (s), 142.8 (s), 147.5 (s).
MS: m/z (relative intensity) = 402 (2) [M+ + 2], 400 (5) [M+],
332 (100). Anal. Calcd for C25H21ClN2O: C, 74.90; H, 5.28;
N, 6.99. Found: C, 74.76; H, 5.18; N, 7.08.
(12) Mikami, T.; Harada, M.; Narasaka, K. Chem. Lett. 1999,
425.
(13) Comasseto, J. V.; Ferreira, J. T. B.; Brandt, C. A.;
Petragnani, N. J. Chem. Res., Synop. 1982, 212.
(14) For examples of aza-Wittig reactions between phosphazenes
and ketenes see: (a) ref.7 (b) Alajarín, M.; Vidal, A.; Tovar,
F.; Ramírez de Arellano, M. C.; Cossío, F. P.; Arrieta, A.;
Lecea, B. J. Org. Chem. 2000, 65, 3633. (c) Alajarín, M.;
Vidal, A.; Ortín, M.-M. Synthesis 2002, 2393; and
references cited therein.
(15) Pracejus, H.; Wallura, G. J. Prakt. Chem. 1962, 19, 33.
(16) Taylor, E. C.; McKillop, A.; Hawks, G. H. Org. Synth. 1973,
52, 36.
(17) Typical Procedure: A solution of the corresponding
ketenimine 8 (1.5 mmol) in anhyd benzene (100 mL) was
heated under nitrogen at reflux temperature and
(18) Crystallographic data for the structure 10a have been
deposited with the Cambridge Crystallographic Data Centre
as supplementary publication number CCDC 229317.
Copies of the data can be obtained on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (e-mail:
deposit@ccdc.cam.ac.uk).
(19) For articles dealing with persistent nitrogen-centered
radicals see: (a) Nakatsuji, M.; Miura, Y.; Teki, Y. J. Chem.
Soc., Perkin Trans. 2 2001, 738. (b) Miura, Y.; Momoki,
M.; Fuchikami, T.; Teki, Y.; Itoh, K.; Mizutani, H. J. Org.
Chem. 1996, 61, 4300. (c) Roberts, J. R.; Ingold, K. U. J.
Am. Chem. Soc. 1973, 95, 3228. (d) Griller, D.;
tris(trimethylsilyl)silane (0.56 g, 2.25 mmol) and AIBN
(0.098 g, 0.6 mmol) were added. Further additions of
tris(trimethylsilyl)silane and AIBN were made as follows: 1)
after 4 h since the first addition, tris(trimethylsilyl)silane
(0.19 g, 0.75 mmol) and AIBN (0.098 g, 0.6 mmol) and 2) 4
h later, tris(trimethylsilyl)silane (0.37 g, 1.5 mmol) and
AIBN (0.098 g, 0.6 mmol). After 16 h since the last addition
the solvent was removed under reduced pressure and the
Mendenhall, G. D.; van Hoof, W.; Ingold, K. U. J. Am.
Chem. Soc. 1974, 96, 6068.
Synlett 2004, No. 6, 991–994 © Thieme Stuttgart · New York