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SCHEME 1. Previous Studies on Ru- and Rh-Catalyzed Reac-
tions of Oxabenzonorbornadiene 1a
Isomerization of 7-Oxabenzonorbornadienes into
Naphthols Catalyzed by [RuCl2(CO)3]2
Melissa Ballantine, Michelle L. Menard, and William Tam*
Guelph-Waterloo Centre for Graduate Work in Chemistry and
Biochemistry, Department of Chemistry, University of
Guelph, Guelph, Ontario, Canada N1G 2W1
Received July 13, 2009
tadienyl, COD=cyclooctadienyl), a [2 þ 2] cycloaddition
is observed and cyclobutene cycloadduct 2 is formed.4
When oxabenzonorbornadiene 1a is treated with the
secondary propargylic alcohol 7 in the presence of the
neutral Ru catalyst Cp*Ru(COD)Cl in MeOH or using a
cationic Ru catalyst (e.g., [CpRu(CH3CN)3]PF6), iso-
chromene 3 is formed.5 On the other hand, if the same
reaction between oxabenzonorbornadiene 1a and the
secondary propargylic alcohol 7 is carried out with
Cp*Ru(COD)Cl in THF, cyclopropane 4 is produced.6
More recently, we have observed that in the absence of an
alkyne, Cp*Ru(COD)Cl catalyzes the isomerization of
oxabenzonorbornadiene 1a to the corresponding
naphthalene oxide 5 when neutral alumina was used in
the workup and to 1-naphthol 8a when silica was used in
the workup.7 We have also reported that asymmetric
cationic rhodium(I)-catalyzed cyclodimerization of oxa-
benzonorbornadiene 1a produced dimers 6 in excellent
enantioselectivity (up to 99% ee).8
Ruthenium-catalyzed isomerization of 7-oxanorborna-
dienes into naphthols was investigated. Among the var-
ious ruthenium catalysts tested, [RuCl2(CO)3]2 gave the
highest yields in the isomerization, and various substi-
tuted naphthols were synthesized in moderate to excellent
yields. Both symmetrical and unsymmetrical 7-oxanor-
bornadienes were employed in the study, and moderate to
excellent regioselectivities were observed.
Oxabicyclic alkenes are valuable synthetic intermedi-
ates as they can serve as a general template to create
highly substituted ring systems.1 For instance, asym-
metric ring-opening of these alkenes allows for the for-
mation of several stereocenters in a single step.2,3 We
have recently investigated different modes of transition-
metal-catalyzed reactions of oxabenzonorbornadiene 1a
and found that, depending on the reaction conditions,
several products (2-6) could be obtained (Scheme 1). For
example, when oxabenzonorbornadiene 1a is treated with
an alkyne in the presence of the ruthenium catalyst,
Cp*Ru(COD)Cl (Cp* = 1,2,3,4,5-pentamethylcyclopen-
Brønsted acid catalyzed isomerization of 7-oxabenzonor-
bornadienes into1-naphthols isa well-knownprocedureanda
valuable method for incorporating a naphthol fragment in
more complex molecules.9 Similar isomerization has been
(4) For selected examples of our recent studies of Ru-catalyzed [2 þ 2]
cycloadditions of bicyclic alkenes and alkynes, see: (a) Villeneuve, K.; Tam,
W. Angew. Chem., Int. Ed. 2004, 43, 610–613. (b) Burton, R. R.; Tam, W.
Tetrahedron Lett. 2006, 47, 7185–7189. (c) Burton, R. R.; Tam, W. J. Org.
Chem. 2007, 72, 7333–7336. (d) Allen, A.; Villeneuve, K.; Cockburn, N.;
Fatila, E.; Riddell, N.; Tam, W. Eur. J. Org. Chem. 2008, 4178–4192.
(5) (a) Villeneuve, K.; Tam, W. Eur. J. Org. Chem. 2006, 5499–5435. (b)
Villeneuve, K.; Tam, W. Organometallics 2007, 26, 6082–6090.
(6) Villeneuve, K.; Tam, W. Organometallics 2006, 25, 843–848.
(7) Villeneuve, K.; Tam, W. J. Am. Chem. Soc. 2006, 128, 3514–3515.
Note that in our previous work using Cp*Ru(COD)Cl that we synthesized,
8a was obtained in 91%. However, in our present study when we use
commercially available Cp*Ru(COD)Cl (from Strem), the highest yield we
could obtain was 67%.
(1) For reviews, see: (a) Rayabarapu, D. K.; Cheng, C. -H. Acc. Chem.
Res. 2007, 40, 971–983. (b) Lautens, M.; Fagnou, K.; Heibert, S. Acc. Chem.
Res. 2003, 36, 48–58.
(2) For selected examples of ring-opening reactions of 7-oxabicyclo-
[2.2.1]heptenes, see: (a) Padwa, A.; Wang, Q. J. Org. Chem. 2006, 71,
7391–7402. (b) Cho, Y.; Zunic, V.; Senboku, H.; Olsen, M.; Lautens, M. J.
Am. Chem. Soc. 2006, 128, 6837–6846. (c) Chen, C. L.; Martin, S. F. J. Org.
Chem. 2006, 71, 4810–4818. (d) Wu, M. -S.; Jeganmohan, M.; Cheng, C.
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Chem. Soc. 2004, 126, 1437–1447. (f) Leong, P.; Lautens, M. J. Org. Chem.
2004, 69, 2194–2196. (g) Zhang, T. -K.; Yuan, K.; Hou, X. -L. J.
Organomet. Chem. 2007, 692, 1912–1919.
(3) For selected examples of ring-opening reactions of 7-oxabicyclo-
[3.2.1]octenes, see: (a) Lautens, M.; Colucci, J. T.; Hiebert, S.; Smith, N.
D.; Bouchain, G. Org. Lett. 2002, 4, 1879–1882. (b) Lautens, M.; Rovis, T. J.
Am. Chem. Soc. 1997, 119, 11090–11091. (c) Lautens, M.; Ma, S.; Chiu, P. J.
Am. Chem. Soc. 1997, 119, 6478–6487. (d) Lautens, M.; Chiu, P.; Ma, S.;
Rovis, T. J. Am. Chem. Soc. 1995, 117, 532–533. (e) Lautens, M.; Abd-El-
Aziz, A. S.; Lough, A. J. Org. Chem. 1990, 55, 5305–5306.
(8) Allen, A.; Le Marquand, P.; Burton, R.; Villeneuve, K.; Tam, W. J.
Org. Chem. 2007, 72, 7849–7857.
(9) (a) Kaelin, D. E.; Lopez, O.; Martin, S. F. J. Am. Chem. Soc. 2001,
123, 6937–6938. (b) Apsel, B.; Bender, J. A.; Escobar, M.; Kaelin, D. E.;
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Kaelin, D. E.; Sparks, S. M.; Plake, H. R.; Martin, S. F. J. Am. Chem. Soc.
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Published on Web 09/02/2009
DOI: 10.1021/jo901504n
r
2009 American Chemical Society