630
I. Montgomery et al. / Tetrahedron Letters 49 (2008) 628–630
Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2001, 123, 3137–
O
O
+
HB
Br
3138; (f) Lee, E.; Han, H. O. Tetrahedron Lett. 2002, 43, 7295–7296;
(g) Dressel, M.; Aechtner, T.; Bach, T. Synthesis 2006, 2206–2214; (h)
Bowman, W. R.; Fletcher, A. J.; Pedersen, J. M.; Lovell, P. J.;
Elsegood, M. R. J.; Lopez, E. H.; McKee, V.; Potts, G. B. S.
Tetrahedron 2007, 63, 191–203.
7
18
19
ClRh(PPh3)3
O
1. (Me3Si)3SiH
OH
21 (66%)
+
B
Br
H
9. (a) Davies, A. G.; Roberts, B. P. J. Chem. Soc., Chem. Commun. 1969,
699; (b) Davies, A. G.; Roberts, B. P. J. Organomet. Chem. 1969, 19,
P17–P18; (c) Davies, A. G.; Griller, D.; Roberts, B. P. J. Chem. Soc. B
1971, 1823–1829; (d) Krusic, P. J.; Kochi, J. K. J. Am. Chem. Soc.
1969, 91, 3942–3944; (e) Brown, H. C.; Midland, M. M. Tetrahedron
1987, 43, 4059–4070.
O
7
7
Br
7
2. 19, ClRh(PPh3)3
18
20
3. H2O2, NaOH
Scheme 3. Radical reduction of 18 initiated by borole 20, followed by
sequential hydroboration and oxidation to give 1-decanol (21).
10. Renaud, P.; Ollivier, C. Chem. Rev. 2001, 101, 3415–3434.
11. (a) Ollivier, C.; Renaud, P. Chem. Eur. J. 1999, 5, 1468–1473; (b)
Ollivier, C.; Renaud, P. Angew. Chem., Int. Ed. 2000, 39, 925–928; (c)
Schaffner, A.-P.; Becattini, B.; Ollivier, C.; Weber, V.; Renaud, P.
Synthesis 2003, 17, 2740–2742; (d) Schaffner, A.-P.; Renaud, P.
Angew. Chem., Int. Ed. 2003, 42, 2658–2660.
12. For examples, of radical reactions initiated by 9-BBN (3) or 4 see: (a)
Chung, T. C.; Janvikul, W.; Lu, H. L. J. Am. Chem. Soc. 1996,
118, 705–706; (b) Masuda, Y.; Hoshi, M.; Nunokawa, Y.; Arase, A. J.
Chem. Soc., Chem. Commun. 1991, 1444–1445; (c) Tamara
Perchyonok, V.; Schiesser, C. H. Tetrahedron Lett. 1998, 39, 5437–
5438.
In summary, PBD (8) and related derivatives are shown
to initiate various radical reactions under mild conditions.
The mechanism of initiation is likely to involve cleavage of
the C–B bond in 8, on reaction with O2, to give a propyl
radical. In comparison to Et3B, PBD and related com-
pounds are easier to handle and they can give more repro-
ducible results. The facile preparation of boroles, by
hydroboration of alkenes, means that this family of com-
pounds could find wide application as radical initiators.
13. For hydroboration using Wilkinson’s catalyst see: (a) Evans, D. A.;
Fu, G. C.; Hoveyda, A. H. J. Am. Chem. Soc. 1988, 110, 6917–6918;
(b) Evans, D. A.; Fu, G. C.; Hoveyda, A. H. J. Am. Chem. Soc. 1992,
114, 6671–6679.
Acknowledgement
We thank the University of York for funding.
References and notes
14. Cyclohexene (0.05 ml, 0.49 mmol, 0.2 equiv) was stirred with Wilkin-
son’s catalyst (0.005 g, 5 mol %), under N2, then catecholborane
(0.58 ml, 1 M in THF, 0.58 mmol, 0.24 equiv) was added dropwise at
0 °C. The mixture was then allowed to warm to rt and stirred. After
4 h, HSnBu3 (0.76 ml, 2.82 mmol, 1.1 equiv) and bromoacetophenone
(1) (0.50 g, 2.50 mmol, 1 equiv) were added and the reaction stirred
overnight in air. Purification by column chromatography (KF on
silica; petrol–EtOAc, 1:1) gave acetophenone (0.39 g, 99%) as a
colourless oil. (Catechol byproducts may be removed from the
organic product, prior to chromatography, by washing a solution of
the crude product in EtOAc with 1 M NaOH).
15. PBD (8) is more stable to oxidation in air than Et3B. After exposure
to air for 72 h, the 1H NMR spectrum indicated mainly unreacted
PBD.
16. De Buyck, L.; Forzato, C.; Ghelfi, F.; Mucci, A.; Nitti, P.; Pagnoni,
U. M.; Parsons, A. F.; Pitacco, G.; Roncaglia, F. Tetrahedron Lett.
2006, 47, 7759–7762.
1. (a) Yorimitsu, H.; Shinokubo, H.; Oshima, K. Synlett 2002, 674–686;
(b) Yorimitsu, H.; Shinokubo, H.; Matsubara, S.; Oshima, K.;
Omoto, K.; Fujimoto, H. J. Org. Chem. 2001, 66, 7776–7785; (c)
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2711.
2. (a) Kihara, N.; Ollivier, C.; Renaud, P. Org. Lett. 1999, 1, 1419–1422;
(b) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Am. Chem. Soc. 2005,
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3. Spiegel, D. A.; Wiberg, K. B.; Schacherer, L. N.; Medeiros, M. R.;
Wood, J. L. J. Am. Chem. Soc. 2005, 127, 12513–12515.
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´
64, 403–409; (b) Beraud, V.; Gnanou, Y.; Walton, J. C.; Maillard, B.
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Jang, Y.-J.; Ko, S.; Fang, H.; Liu, J.-T.; Yao, C.-F. Tetrahedron Lett.
2006, 47, 6133–6137.
17. Tetrahydrofuran 16 was obtained in similar yield using (Me3Si)3SiH
(1.1 equiv) in place of Bu3SnH (1.1 equiv).
18. For polymerisation of alkenes using borane initiators see: (a) Zhang,
Z.-C.; Chung, T. C. M. Macromolecules 2006, 39, 5187–5189; (b)
Kanno, S.; Hosoi, M.; Ogata, T.; Takeishi, M. Polym. Int. 1997, 42,
321–327.
5. (a) Miyabe, H.; Ueda, M.; Yoshioka, N.; Naito, T. Synlett 1999, 465–
467; (b) Miyabe, H.; Yamaoka, Y.; Takemoto, Y. J. Org. Chem. 2005,
70, 3324–3327; (c) Yoshimitsu, T.; Arano, Y.; Nagaoka, H. J. Org.
Chem. 2005, 70, 2342–2345.
19. The average molecular mass (Mn) and polydispersity (PDI) of
polymer samples were obtained using GPC, on a system equipped
with a guard column and two Shodex columns (KF-802.5 and KF-
803), with a Waters 2410 differential refractive index detector using
THF (containing 1% toluene as a marker) at 0.7 ml minÀ1 as eluant.
Mn was calculated against nine narrow PMMA standards in the range
6. Takami, K.; Usugi, S.-i.; Yorimitsu, H.; Oshima, K. Synthesis 2005,
824–839.
7. (a) Charrier, N.; Gravestock, D.; Zard, S. Z. Angew. Chem., Int. Ed.
2006, 45, 6520–6523; (b) Guerrero, M. A.; Miranda, L. D. Tetra-
hedron Lett. 2006, 47, 2517–2520.
8. For some examples see: (a) Satoh, S.; Sodeoka, M.; Sasai, H.;
Shibasaki, M. J. Org. Chem. 1991, 56, 2278–2280; (b) Devin, P.;
Fensterbank, L.; Malacria, M. Tetrahedron Lett. 1999, 40, 5511–5514;
(c) Miyabe, H.; Tanaka, H.; Naito, T. Tetrahedron Lett. 1999, 40,
8387–8390; (d) Miura, K.; Tomita, M.; Yamada, Y.; Hosomi, A. J.
Org. Chem. 2007, 72, 787–792; (e) Fujita, K.; Nakamura, T.;
5.59 Â 105 to 960 g molÀ1
.
20. PBD (8) can be used to polymerise other alkene monomers, at rt,
including butyl acrylate, methyl acrylate, methacrylic acid and
acrylamide. Parsons, A. F.; Sharpe, D. J.; Taylor, P. unpublished
results.