J . Org. Chem. 2001, 66, 4097-4098
4097
Ta ble 1. Cla y-Ca ta lyzed Dep r otection of MOM Eth er sa
Ch ela tion -Con tr olled Selectivity in th e
Cla y-Ca ta lyzed Dep r otection of P h en olic
Meth oxy Meth yl Eth er s
J ay P. Deville and Victor Behar*
Department of Chemistry MS-60, Rice University,
Houston, Texas 77251-1892
Received February 16, 2001
The use of Montmorillonite clay catalysis to effect
1
organic transformations has increased due to its excep-
tionally mild conditions, ease of use and recyclability,
2
simplicity of purification, and low cost. Montmorillonite
clays and their ion-exchanged forms have been used in
a variety of Lewis acid-catalyzed reactions, including the
3
1c
aldol condensation, Prins reaction, Claisen rearrang-
ment,4 and Diels-Alder reaction.5 In connection with
studies to develop selective methods to differentiate
phenolic groups in naphthoquinone- and anthraquinone-
containing antitumor antibiotics with highly oxygenated
frameworks, we observed an unexpectedly facile removal
of a methoxy methyl (MOM) ether catalyzed by Mont-
morillonite K 10 clay (Scheme 1). The reaction of MOM-
6
protected naphthol 1 proceeded at room temperature in
*
To whom correspondence should be addressed. Tel: 713-348-6159.
Fax: 713-348-5155.
1) For comprehensive review of clays used in organic synthesis,
see: (a) Nikalje, M. D.; Phukan, P.; Sudalai, A. Org. Prep. Proc. Int.
000, 32, 1. (b) Balogh, M.; Laszlo, P. In Organic Chemistry Using
Clays; Springer-Verlag: New York, 1993. For recent examples, see:
c) Yadav, J . S.; Reddy, B. V. S.; Kumar, G. M.; Murthy, Ch. V. S. R.
(
2
(
Tetrahedron Lett. 2001, 42, 89. (d) Choudary, B. M.; Chowdari, N. S.;
Kantam, M. L. Tetrahedron 2000, 56, 7291. (e) Das, B.; Madhusudhan,
P.; Venkataiah, B. Synth. Commun. 2000, 30, 4001.
(2) Montmorillonite K 10 and Montmorillonite KSF clays are both
available from Aldrich for $20.25/kg.
(
3) Loh, T.-P.; Li, X.-R. Tetrahedron 1999, 55, 10789.
(4) Dauben, W. G.; Cogen, J . M.; Behar, V. Tetrahedron Lett. 1990,
3
1, 3241.
5) Adams, J . M.; Dyer, S.; Martin, K.; Matear, W. A.; McCabe, R.
W. J . Chem. Soc., Perkin Trans. 1 1994, 761.
6) MOM-protected naphthol 1 was available in three steps from
(
(
known 2-bromo-5,8-dimethoxy-1-naphthol by (1) MOM protection; (2)
lithium-halogen exchange, quenching with trimethylborate, followed
by an oxidative workup; and (3) allylation of the resultant phenol. (a)
Laatsch, H. Liebigs Ann. Chem. 1985, 2420. (b) Maddaford, S. P.;
Andersen, N. G.; Cristofoli, W. A.; Keay, B. A. J . Am. Chem. Soc. 1996,
1
18, 10766.
7) Entry 1: (a) Brand, K.; Schueber, W. Chem. Ber. 1942, 75, 156.
(
Entries 2 and 4: (b) Mabic, S.; Vaysse, L.; Benezra, C.; Lepoittevin, J .
P. Syn. 1999, 1127. Entry 3: (c) Versteeg, M.; Bezuidenhoudt, B.;
Ferreira, D. Heterocycles 1993, 36, 1743. Entry 5: (d) Yamauchi, S.;
Taniguchi, E. Agric. Biol. Chem. 1991, 55, 3075. (e) Ahmad, F. B. H.;
Bruce, J . M. Synth. Commun. 1994, 24, 1639. Entry 6: (f) Dunn, B.
M. Bruice, T. C. J . Am. Chem. Soc. 1971, 93, 5725. Entry 7: (g)
Christensen, H. Synth. Commun. 1975, 5, 65. Entry 8: (h) Cruz-
Almanza, R.; Perez-Flores, F.; Lemini, C. Heterocycles 1994, 37, 759.
Entry 9: (i) Fukuyama, T.; Frank, R. K.; J ewell, C. F. J . Am. Chem.
Soc. 1980, 102, 2122. Entry 10: (j) Ranu, B. C.; Majee, A.; Das, A. R.
Synth. Commun. 1995, 25, 363. Entry 11: (k) Lunney, E. A.; Hagen,
S. E.; Domagala, J . M.; Humblet, C.; Kosinski, J .; Tait, B. D.; Warmus,
J . S.; Wilson, M.; Ferguson, D.; Hupe, D.; Tummino, P. J .; Baldwin,
E. T.; Bhat, T. N.; Liu, B.; Erickson, J . W. J . Med. Chem. 1994, 37,
a
All entries and their deblocked products are known com-
pounds.7
aldehyde is removed.
prolonged exposure to the clay at 50 °C. No reaction was observed
at 25 °C.
b
Isolated yield. Only the MOM group ortho to the
c
d
Complex decomposition occurred with
benzene over 45 min, affording 95% isolated yield of
phenol 2.
Recognizing the potential utility of this mild method
for removal of the MOM protecting group, we sought to
study the scope of this reaction. The results are sum-
marized in Table 1.
2
664. Entry 12: (l) Sham, H. L.; Zhao, C.; Stewart, K. D.; Betebenner,
D. A.; Lin, S.; Park, C. H.; Kong, X. -P.; Rosenbrook, W.; Herrin, T.;
Madigan, D.; Vasavanonda, S.; Lyons, N.; Molla, A.; Saldivar, A.;
Marsh, K. C.; McDonald, E.; Wideburg, N. E.; Denissen, J . F.; Robins,
T.; Kempf, D. J .; Plattner, J . J .; Norbeck, D. W. J . Med. Chem. 1996,
The reaction was found to be general for a variety of
ortho-substituted MOM-protected phenols (entries 1-6),
3
9, 392.
1
0.1021/jo015578l CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/28/2001