A. D. Bailey et al. / Tetrahedron Letters 49 (2008) 691–694
693
Table 1 (continued)
Entry
Substratea
Productb
NRf
mol % BiI3
10.0
Timec and temp
3 h, rt
Yieldd (%)
OTBDMS
OTBDMS
16
Ph
17
NRf
1.0
1 h 30 min, rt
O
O
a
Acetals were either purchased commercially or synthesized by a previously reported method.10
All products have been previously reported and were characterized by 1H and 13C NMR spectroscopy.
Reaction progress was followed by GC, TLC, or 1H NMR.
b
c
d
Refers to yield of the isolated product. The crude product was found to be >98% pure unless mentioned otherwise and hence further purification was
deemed unnecessary.
e
GC analysis indicated that the crude product is 96% pure.
Starting material was recovered unchanged.
f
these conditions no deprotection was observed and the
starting dioxolane was recovered. The deprotection of cit-
ral dimethyl acetal (entry 10) using 1.0 mol % BiI3 in the
presence of proton spongeTM [1,8-(dimethylamino)naphtha-
lene]9 was also unsuccessful. These results suggest that it is
unlikely that the hydrolysis is catalyzed primarily by coor-
dination of Bi3+ to the acetal oxygen and rather point to
the role of HI in the deprotection. The deprotection of both
2-(3-bromophenyl)-1,3-dioxolane (entry 14) and citral
dimethyl acetal (entry 10) was carried out successfully at
room temperature using 3.0 mol % HI in water. Although
the available evidence suggests that HI plays an active role
in the reaction, the use of bismuth iodide remains a more
attractive option than HI because it is non-corrosive and
easier to dispense in contrast to hydriodic acid.
References and notes
1. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; John Wiley and Sons: New York, 1999; (b)
Hanson, J. R. Protecting Groups in Organic Synthesis, 1st ed.;
Blackwell Science: Malden, MA, 1999; (c) Kocienski, P. J. Protecting
Groups, 1st ed.; Georg Thieme: Stuttgart, 1994.
2. p-TsOH/acetone: (a) Colvin, E. W.; Raphael, R. A.; Roberts, J. S. J.
Chem. Soc., Chem. Commun. 1971, 858; 50% Trifluoroacetic acid in
CHCl3–H2O: (b) Ellison, R. A.; Lukenbach, E. R.; Chiu, C.-W.
Tetrahedron Lett. 1975, 16, 499; LiBF4: (c) Lipshutz, B. H.; Harvey,
D. F. Synth. Commun. 1982, 12, 267; Amberlyst-15/aqueous acetone:
(d) Coppola, G. M. Synthesis 1984, 1021; aqueous DMSO: (e)
Kametani, T.; Kondoh, H.; Honda, T.; Ishizone, H.; Suzuki, Y.;
Mori, W. Chem. Lett. 1989, 18, 901; Bi(NO3)3Á5H2O: (f) Eash, K. J.;
Pulia, M. S.; Wieland, L. C.; Mohan, R. S. J. Org. Chem. 2000, 65,
8399; (g) Sabitha, G.; Babu, R. S.; Reddy, E. V.; Yadav, J. S. Chem.
Lett. 2000, 29, 1074.
A representative procedure is given here: A mixture of
trans-cinnamaldehyde dimethyl acetal (0.5064 g, 2.84
mmol) in H2O (5.0 mL) was stirred as BiI3 (0.0168 g,
0.0284 mmol, 1.0 mol %) was added. The reaction was
monitored by TLC (EtOAc/hexanes, 20/80, v/v). After
1 h 40 min, EtOAc (40.0 mL) was added to the reaction
mixture and the biphasic mixture was filtered through a
bed of Celite. The aqueous layer from the filtrate was
extracted with EtOAc (20 mL) and the combined organic
layers were washed with 5% aqueous Na2S2O3 (10 mL),
10% aqueous Na2CO3 (10 mL), saturated aqueous NaCl
(10 mL), and dried (Na2SO4). The solvent was removed
on a rotary evaporator to yield 0.3403 g (91%) of a clear
liquid that was identified to be trans-cinnamaldehyde by
1H and 13C NMR spectroscopy. The purity of the crude
product was determined to be >98% by 1H and 13C
NMR as well as GC analysis.
´
3. TiCl4: (a) Balme, G.; Gore, J. J. Org. Chem. 1983, 48, 3336;
FeCl3Á6H2O on silica gel: (b) Kim, K. S.; Song, Y. H.; Lee, B. H.;
Hahn, C. S. J. Org. Chem. 1986, 51, 404; Ph3P/CBr4: (c) Johnstone, C.;
Kerr, W. J.; Scott, J. S. J. Chem. Soc., Chem. Commun. 1996, 341;
CeCl3: (d) Marcantoni, E.; Nobili, F.; Bartoli, G.; Bosco, M.; Sambri,
L. J. Org. Chem. 1997, 62, 4183; FeCl3Á6H2O: (e) Sen, S. E.; Roach, S.
L.; Boggs, J. K.; Ewing, G. J.; Magrath, J. J. Org. Chem. 1997, 62,
6684; TMSN(SO2F)2: (f) Kaur, G.; Trehan, A.; Trehan, S. J. Org.
´
Chem. 1998, 63, 2365; Ceric ammonium nitrate: (g) Marko, I. E.; Ates,
A.; Gautier, A.; Leroy, B.; Plancher, J.-M.; Quesnel, Y.; Vanherck,
J.-C. Angew. Chem., Int. Ed. 1999, 38, 3207; Bi(OTf)3Á4H2O: (h)
Carrigan, M. D.; Sarapa, D.; Smith, R. C.; Wieland, L. C.; Mohan, R.
S. J. Org. Chem. 2002, 67, 1027; (i) Dalpozzo, R.; De Nino, A.;
Maiuolo, L.; Procopio, A.; Tagarelli, A.; Sindona, G.; Bartoli, G. J.
Org. Chem. 2002, 67, 9093; b-Cyclodextrin: (j) Krishnaveni, N. S.;
Surendra, K.; Reddy, M. A.; Nageswar, Y. V. D.; Rao, K. R. J. Org.
Chem. 2003, 68, 2018; HClO4/silica gel: (k) Agarwal, A.; Vankar, Y.
D. Carbohydr. Res. 2005, 340, 1661; I2 (l) Sun, J.; Dong, Y.; Cao, L.;
Wang, X.; Wang, S.; Hu, Y. J. Org. Chem. 2004, 69, 8932; CuSO4/NaI:
(m) Bailey, A. D.; Cherney, S. M.; Anzalone, P. W.; Anderson, E. D.;
Ernat, J. J.; Mohan, R. S. Synlett 2006, 215.
In summary, a chemoselective method for the deprotec-
tion of acetals and ketals catalyzed by bismuth(III) iodide
in H2O has been developed.
4. Most bismuth(III) compounds have an LD50 value that is comparable
to or even less than that of NaCl (see Ref. 6c).
5. (a) Irwing-Sax, N.; Bewis, R. J. Dangerous Properties of Industrial
Materials; Van Nostrand Reinhold: New York, 1989; pp 283–284,
522–523; (b) The Chemistry of Organic Arsenic, Antimony and Bismuth
Compounds; Dill, K., McGown, E. L., Patai, S., Eds.; J. Wiley: New
York, 1994; pp 695–713; (c) The Chemistry of Organic Arsenic,
Antimony and Bismuth Compounds; Worsmer, U., Nir, I., Patai, S.,
Eds.; J. Wiley: New York, 1994; pp 715–723; (d) Chemistry of Arsenic,
Antimony and Bismuth; Reglinski, J., Norman, N. C., Eds.; Blackie
Academic and Professional: New York, 1998; pp 403–440.
Acknowledgments
The authors gratefully acknowledge funding from the
National Science Foundation for a RUI (Research in
Undergraduate Institutions) Grant (# 0650682) awarded
to R.S.M.