10.1002/ejoc.201901239
European Journal of Organic Chemistry
FULL PAPER
temperature for 18 h. The mixture was then filtered on celite (washed with
ethyl acetate) and the filtrate was washed with hydrochloric acid (1M) and
brine, dried over sodium sulfate, filtered and concentrated under reduced
pressure to give then expected product 2 in high yield (99%).
The method also displays good chemoselectivity. For example,
we synthesized a compound containing both benzodioxolane and
alkylarylether 25 (entry 13). In the presence of the thiol reagent,
disubstituted acetal is cleaved selectively without affecting the
alkyl ether bond. In general, alkyl protected phenol are stable
under these conditions. However, other protecting groups of
phenols or aliphatic amine are removed under our standard
procedure. For example, the 2,4-dinitrophenylsulfonyl group has
been used to protect the hydroxyl function of phenols (e.g., 49) or
the α-amino function of amino acids (e.g., 51).[16] This group is
labile under our conditions, cleaving the protecting group of 49
and 51, to give high yield of the corresponding phenol 50, or
amino acid 52 (Scheme 3).
Acknowledgments
We appreciate the reading of this manuscript by Dr. Christopher
Penney. We also thank Mrs. Lyne Marcil for the skillful preparation
of this manuscript, and the department of mass spectra at McGill
University for the HRMS analysis.
Keywords: Acetals • N,O-acetal • SiliaMetS® • Thiol solid
support • Catechol
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aliphatic amine using Si-Thiol.
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Conclusions
In conclusion, a practical, efficient and general method was
developed for the deprotection of a variety of aromatic and
aliphatic acetals to their corresponding catechol or diol derivatives
using thiol functionalized on silica. The method is mild and
amenable to scale-up. It does not require an inert atmosphere and
clean conversions were observed. It offers the advantage of a
general route with high yield which can be undertaken at ambient
temperature. The advantages of using thiol bound on silica gels
are the following: (i) toxic or difficult to remove reagents and by-
products are immobilized and can be separated from the product
by a simple filtration; (ii) the reaction is devoid of thiol stench, and
(iii) use of solvent independent, thermally stable reagents and
easy work up procedure. Furthermore, as in many of our
examples purification by chromatography was unnecessary, the
amount of solid waste is reduced compared to other methods.
Indeed, future work on the regeneration of the thiol groups on
silica from the corresponding thioacetals[17] produced by the
reaction could allow reuse of the solid-supported thiol.
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Experimental Section
Typical Procedure for the deprotection of acetals (1)
A mixture of 2,2-dimethyl-1,3-benzodioxole 1 (50 mg, 0.33 mmol) and Si-
Thiol (1.37 mmol/g; 0.48 g, 0.664 mmol) in dichloromethane (5 mL) was
treated with BF3•OEt2 (42 μL, 0.33 mmol). The mixture was stirred at room
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