10.1002/ejoc.201800292
European Journal of Organic Chemistry
COMMUNICATION
to the best of our knowledge, the first example of Sc(III)-
catalyzed oxidative transformations using DIB 8. The present
method potentially serves as α-hydroxylation of a wide range of
carbonyl compounds with acid/base sensitive functionalities.
Further studies to optimization of iodoarene-catalyzed
acetoxylation are in progress in our laboratory.
Aid for Challenging Exploratory Research (No. 16K15097) (to K.
M.).
Keywords: Hypervalent • Iodine • Acetoxylation • Docetaxel •
Catalyst reuse
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Experimental Section
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T. Mandai, PCT Int. Appl. 2017, WO2017006573.
General procedure for oxidative acetoxylation of 1. A typical
example (Table 2, entry 4). To a stirred solution of 1 (33 mg, 0.1 mmol),
Sc2O3 (0.2 mg, 0.0015 mmol), and 8 (38.7 mg, 0.12 mmol) in acetic acid
(1.0 mL) was slowly added TMSOTf (7.2 μL, 0.04 mmol) at room
temperature under argon and the mixture was stirred for 40 h. The
reaction mixture was then added excess hexane and vigorously stirred at
room temperature for 10 min. After separation of supernatant from the
mixture, the residue was extracted with hexane (1 mL) three times. The
residue can be used for further reaction without any treatment. A
combined organic layer was concentrated under an aspiratory vacuum to
give an oil. 1H NMR analysis (internal standard: tert-butyl methyl ether)
showed the formation of acetate 9 and triflate 10, in 56% and 39%,
respectively. Because of the labile nature, 10 could not be isolated as a
pure form. 10: 1H NMR (400 MHz, CDCl3) δ; 0.55 (d, J = 6.9 Hz, 3H for
one isomer), 0.68 (d, J = 6.9 Hz, 3H), 0.72 (d, J = 6.9 Hz, 3H), 0.62–0.71
(m, 1H), 0.79 (d, J = 6.5 Hz, 3H), 0.70–0.85 (m, 1H), 0.91–1.1 (m, 1H),
1.21–1.49 (m, 2H), 1.50–1.75 (m, 3H), 1.78–1.88 (m, 1H), 1.98–2.05 (m,
1H), 4.09 (s, 3H for one isomer), 4.10 (s, 3H for another isomer), 4.65–
4.80 (m, 3H), 6.66 (s, 3H for one isomer), 6.68 (s, 3H for another isomer),
7.30–7.50 (m, 3H), 7.60–7.67 (m, 2H). ESI-MS (positive) m/z: 502
[(M+Na)+]. For isolation of 9, the residue was added sodium acetate (8.2
mg, 0.1 mmol) in DMSO (1 mL) and stirred at room temperature for 3 h.
The mixture was poured into water and extracted with CH2Cl2 four times.
Combined organic layer was washed with water, dried over Na2SO4,
filtered, and concentrated under an aspiratory vacuum to give an oil,
which was purified by preparative TLC (hexane/ethyl acetate = 9:1, Rf =
0.4), to give 9 (29.5 mg, 82%) as a colorless oil. Acetate 9 was obtained
as a mixture of stereoisomers (ca. 1:1 mixture of (S)- and (R)-isomers at
the α-position (denoted as (S)-9 and (R)-9) and oxime E/Z–mixtures): IR
M. Presset, D. Mailhol, Y. Coquerel, J. Rodriguez, Synthesis 2011,
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1
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(neat) ν cm-1; 2955, 2869, 1747, 1616, 1445, 1370, 1210, 1046, 700. H
NMR (400 MHz, CDCl3) δ; 0.44 (d, J = 6.9 Hz, 1H for (R)-9), 0.62–0.71
(m, 1H), 0.68 (d, J = 6.9 Hz, 3H), 0.72 (d, J = 6.9 Hz, 3H), 0.79 (d, J = 6.5
Hz, 3H), 0.70–0.85 (m, 1H), 0.87 (d, J = 7.0 Hz, 3H for (R)-9), 0.88 (d, J
= 6.5 Hz, 3H for (S)-9), 0.91–1.10 (m, 1H), 1.21–1.49 (m, 2H), 1.54–1.67
(m, 3H), 1.81–1.89 (m, 1H for (R)-9), 1.97–2.03 (m, 1H for (S)-9), 2.15 (s,
3H for (S)-9), 2.17 (s, 3H for (R)-9), 4.04 (s, 3H), 4.65 (td, J = 10.9, 4.5
Hz, 1H for (R)-9), 4.67 (td, J = 10.9, 4.5 Hz, 1H for (S)-9), 6.74 (s, 1H),
7.32–7.40 (m, 3H), 7.60–7.64 (m, 2H for (S)-9), 7.65–7.69 (m, 2H for (R)-
9). 13C NMR (125 MHz, CDCl3) δ; 20.15, 20.18, 21.21, 21.4, 22.2, 22.4,
23.5, 24.5, 24.6, 25.5, 25.6, 30.7, 31.8, 34.0, 35.0, 46.2, 47.2, 49.6,
62.07, 62.14, 63.2, 63.3, 64.7(2C), 65.86, 65.93, 126.3, 126.5, 126.7,
127.5, 127.7, 127.8, 127.96, 128.0, 128.84, 128.9, 129.1, 130.1, 130.2,
133.0, 133.1, 166.7, 166.9, 169.5. MS m/z (relative intensity): 207 (13%,
[M-(mentylCO2)+]), 165 (11), 138 (8), 134 (27), 103 (40), 83 (100), 77
(13). HRMS (ESI, positive) m/z calcd for C22H31NNaO5 [(M+Na)+]:
412.2100; found 412.2091.
[14] See Supporting Information (Scheme S1).
[15] M. Ochiai, Y. Takeuchi, T. Katayama, T. Sueda, K. Miyamoto, J. Am.
Chem. Soc. 2005, 127, 12244–12245.
[16] Data
taken
from
TCI
America:
[17] J. A. McCleverty, T. J. Meyer, Comprehensive Coordination Chemistry
II, Elsevier Science: Amsterdam, 2003.
[18] Sc2O3 (4 X 103 $/mol, Aldrich), TMSOTf (3 X 102 $/mol, TCI America).
[19] Catalyst maintained high activity even after five runs in
dichloromethane (Scheme S2).
[20] Slow recrystallization of deprotected product from hexane selectively
afforded pure (S)-3 with S-configuration at hydroxy-α-carbon atom. See
also reference [2].
[21] X-ray data for 3: C20H29NO4, M = 389.49, T = 173 K, orthorhombic,
space group P212121 (No. 19), a = 9.1946(5) ꢁ, b = 12.0882(8) ꢁ, c =
17.1926(10) ꢁ, V = 1910.9(2) ꢁ3, Z = 4, Dc = 1.208 g cm-3, μ(Mo Kα) =
14.819 cm-1. 4363 reflections were collected; 2484 were unique. R =
0.0753, wR2 = 0.2112. Crystallographic data have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC-1558744.
Acknowledgements ((optional))
Text. This work was supported by JSPS Grant-in-Aid for
Scientific Research (B) (No. 17H03017) (to K. M.) and Grant-in-
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