LETTER
Ytterbium Triflate Mediated Selective Deprotection of Acetates
1965
washed with water (2 x 5 ml), dried (Na2SO4) and evaporated
to get 6-hydroxyhexyl pivaloate (0.481g) in 97% yield as an
oily liquid.
Thus, the present study, amply indicated the utility of
ytterbium triflate in IPA at reflux as an effective and high-
ly selective system for a) selectivity between deacetyla-
tion vs. Fries migration of aryl acetates, b) deacetylation
of a wide variety of acetates, c) differentiating primary ac-
etate over secondary acetate, benzoate and pivaloate; sec-
ondary acetate over primary benzoate and phenolic
acetate over acetamide. Thus the order of selectivity is:
primary acetate > secondary acetate and primary benzoate
> pivaloate. Thus the present method of deacetylation
with good selectivity would find use in organic synthesis.
Spectral data for selected compounds (200MHz, CDCl3,
TMS, in ppm):6-hydroxyhexyl pivaloate:1H NMR: δ 1.22 (s,
9H, 3CH3) 1.4-1.52 (m, 4H, 2 x -CH2), 1.55-1.75 (m, 4H,
2 x -CH2), 2.15 (br.s, 1H, OH), 3.65 (t, 2H, J 9Hz, CH2OH),
4.04 (t, 2H, J 9Hz, CH2); IR (neat): 3480(m), 2950(s), 1725,
1480, 1150. MSEI (m/z,%): 103(13), 85(10), 83(17), 82(41),
67(9). 6-hydroxyhexyl 3,5-dimethoxybenzoate:1H NMR: δ
1.45-1.85 (m, 8H, 4 x CH2), 3.65 (t, 2H, J 9Hz, CH2), 3.85 (s,
6H, 2 x -OCH3), 4.3 (t, 2H, J 9Hz, CH2), 6.6 (t, 1H, J 3.5Hz,
ArH), 7.13 (s, 1H, ArH), 7.15 (s, 1H, ArH); IR (neat):
3425(m), 2905(s), 1725, 1600, 1465, 1150; MSEI (m/z,%):
282 (M+, 6), 183 (43), 165 (18), 139 (9). 5-hydroxy-7,8-
dimethyl-4-propyl-7,8-dihydro-2H,6H-pyrano [3,2 -f]
chromene-2,6-dione: m.p.: 133-134 °C; 1H NMR: 1.03(t, 3H,
J 9Hz, CH3), 1.2-1.38 (m, 3H, CH3), 1.45-1.6 (m, 3H, CH3),
1.62-1.8 (m, 2H, CH2), 2.6-2.75 (m, 1H, CH), 2.92 (t, 2H, J
9Hz, CH2), 4.2-4.36 (m, 0.7H, CH), 4.6-4.75 (m, 0.3H, CH),
5.98 (s, 1H, ArH), 6.38 (s, 1H, COCH), 13.7 (s, 0.3H, OH),
14.0 (s, 0.7H, OH). IR (KBr): 2940(w), 1720(s), 1705, 1625,
1385, 1275. MSEI: 302(M+,100), 287(13), 274(58), 259(59),
246(25), 218(10), 203(10).5-hydroxy-8,9-dimethyl-4-propyl-
9,10-dihydro-2H,8H -pyrano[2,3-f]chromene-2,10-dione:
m.p -210-213°C; 1H NMR:1.01(t, 3H, J 9Hz, CH3), 1.1-1.26
(m, 3H, CH3), 1.35-1.5 (m, 3H, CH3), 1.56-1.76 (m, 2H,
CH2), 2.44 -2.6 (m, 1H, CH), 2.92 (t, 2H, J 9Hz, CH2), 4.14-
4.28 (m, 0.7H, CH), 4.58-4.68 (m, 0.3H, CH), 5.98 (s, 1H,
ArH), 6.36 (s, 1H, COCH), 10.8 (br.s, 1H, OH). IR (KBr):
3430(w), 2960(w), 1750(s), 1725, 1605, 1375. MSEI:302(M+,
82), 287(10), 274(37), 259(33), 246(100), 218(32).
References and Notes
#IICT Communication No. 4295.
(1) Greene, T. W.; Wuts, P.G.M. Protective Groups In Organic
Synthesis; 2nd ed.: John Wiley & sons Inc.: New York 1991.
(2) Baptistella, L.H.B.; dos Santos, J.F.; Ballabio, K.C.;
Marsaioli, A.J. Synthesis 1989, 436 and references cited
therein.
(3) Sharma, G.V.M.; Ilangovan, A.; Mahalingam, A.K. J. Org.
Chem. 1998, 63, 9103.
(4) Marshman, R.W. Aldrichimica Acta 1995, 28, 77.
(5) Hanamoto, T.; Sugimoto Y.; Yokoyama Y.; Inanaga J. J. Org.
Chem. 1996,61, 4491.
(6) Kobayashi. S.; Moriwaki. M.; Hachiya, I. Tetrahedron Lett.
1996, 37, 2053.
(7) Typical experimental procedure: A solution of 6-
acetyloxyhexyl pivaloate (0.5g, 2.04mmol) in isopropyl
alcohol (5ml) was treated with Yb(TOf)3 (0.127g, 0.204
mmol) at reflux temperature for 26h. After completion of
reaction (Tlc analysis, silica gel, 4:1 hexane/ethyl acetate) the
reaction mixture was allowed to cool to room temperature and
solvent was evaporated under reduced pressure to get an oily
residue. The residue was diluted with ethyl acetate (10 ml),
Article Identifier:
1437-2096,E;1999,0,12,1963,1965,ftx,en;L11599ST.pdf
Synlett 1999, No. 12, 1963–1965 ISSN 0936-5214 © Thieme Stuttgart · New York