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DOI: 10.1055/s-0028-1083517
A Novel Method for the Synthesis of Thioacetates Using Benzyltriethylammonium Tetrathiomolybdate and Acetic Anhydride
Publication History
Publication Date:
01 October 2008 (online)

Abstract
Herein we report a simple and efficient methodology for the synthesis of thioacetates using benzyltriethylammonium tetrathiomolybdate and acetic anhydride as the key reagents, starting from alkyl halides in a multistep, tandem reaction process. Its application in the synthesis of orthogonally protected cysteine and anomeric β-thioglycosides has also been demonstrated.
Key words
benzyltriethylammonium tetrathiomolybdate - acetic anhydride - thioacetates
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References and Notes
General Procedure
for the Synthesis of Thioacetates - Synthesis of 4a
To
the solution of alkyl halide 5a (0.169
g, 1 mmol,) in MeCN (5 mL), tetrathiomolybdate 1 (0.37
g, 2.2 equiv) was added and the reaction mixture was stirred for
1 h. To this solution, Ac2O (0.408 g, 4.0 equiv) was
added and the reaction mixture was stirred further for 1.5 h. The
solvent was removed under vacuum, the solid residue was extracted with
CH2Cl2-Et2O (3:7) 5 × 10
mL, filtered through Celite and concentrated. The crude product
was purified by silica gel (100-200 mesh) column chromatography;
EtOAc-hexane (19:1); gummy liquid, yield 94%.
IR (neat): 3030 (w), 2924 (m), 1692 (s), 1353 (w), 1133 (m), 627
(m) cm-¹. ¹H NMR
(300 MHz, CDCl3): δ = 7.27 (s, 5 H),
4.09 (s, 2 H), 2.31 (s, 3 H). ¹³C (75
MHz, CDCl3): δ = 194.8, 137.4, 128.6, 128.4,
127.1, 33.2, 30.1. HRMS: m/z calcd
for C9H10OS: 189.030 [M + Na];
found: 189.0358.
Compound 4d:
oily liquid, yield 96%. IR: 2988 (w), 1676 (s), 1416 (m),
1176 (s), 625 (m) cm-¹. ¹H
NMR (300 MHz, CDCl3): δ = 7.88 (d, J = 8.1 Hz,
2 H), 7.30 (d, J = 8.1
Hz,
2 H), 4.13 (s, 2 H), 2.57 (s, 3 H), 2.35 (s, 3 H). ¹³C
NMR (75 MHz, CDCl3): δ = 197.4, 194.5.
Compound 4l: oily liquid, yield 80%. IR
(neat): 2903 (m), 2863 (w), 1732 (s), 1462 (m), 1110 (s) cm-¹. ¹H
NMR (300 MHz, CDCl3): δ = 2.71 (m,
1 H), 2.37 (s, 3 H), 1.70-1.30 (m, 8 H), 1.00 (t, J = 7.2 Hz,
3 H), 0.91 (t, J = 7.2
Hz, 3 H).
¹³C NMR (75 MHz,
CDCl3): δ = 195.4, 54.4, 33.0, 26.7, 22.5,
13.8, 11.0. HRMS: m/z calcd
for C9H18OS: 197.0976 [M + Na];
found: 197.0970.
Compound 8: white
solid, mp 77 ˚C, yield 80%; [α]D
²8 -48 (c 1, CHCl3). IR (neat): 3351
(br), 2951 (w), 1698 (s), 1517 (m), 1212 (m) cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.33 (m,
5 H), 5.55 (d, J = 7.2
Hz, 1 H), 5.11 (s, 2 H), 4.50-4.60 (m, 1 H), 3.75 (s, 3
H), 3.42 (dd, J = 14.0,
4.8 Hz, 1 H), 3.40 (dd, J = 14.0,
4.8 Hz, 1 H), 2.32 (s, 3 H). ¹³C NMR
(100 MHz, CDCl3): δ = 194.8, 170.5,
155.6, 136.0, 128.4, 128.1, 128.0, 67.0, 53.4, 52.7, 31.1, 30.3.
HRMS: m/z calcd for C14H17O5S:
334.0725 [M + Na]; found 334.0710.
Compound 11: gummy solid, yield 78%; [α]D
²8 +8.7
(c
1, CHCl3). IR
(neat): 3318 (br), 2965 (m), 2930 (m), 1736 (s), 1695 (s), 1682
(s), 1635 (m), 1262 (m), 1213 (m), 1139 (m) cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.34 (s,
5 H), 6.92 (d, J = 8.0
Hz, 1 H), 5.67 (d, J = 8.0
Hz, 1 H), 5.12 (s, 2 H), 4.52 (dd, J = 8.6,
4.8 Hz 1 H), 4.40 (m, 1 H), 3.35 (dd, J = 16.0, 4.0
Hz, 1 H), 3.12 (dd, J = 16.0,
8.0 Hz, 1 H), 2.30 (s, 3 H), 1.90-1.86 (m, 1 H), 1.44-1.36
(m, 1 H), 1.18-1.12 (m, 1 H), 0.90-0.86 (m, 6
H). ¹³C NMR (100 MHz, CDCl3): δ = 196.6, 171.8,169.6,
156.3, 136.0, 128.4, 128.1, 128.0, 67.7, 56.6, 55.0, 52.1, 37.6,
31.4, 30.4, 25.0, 15.3, 11.2. HRMS: m/z calcd
for C20H28N2O8S: 447.1506 [M + Na];
found: 447.1563.
To a solution of dipeptide 9 (1.0 mmol, 0.366 g) and pyridine (5 mmol, 0.395 g) in CH2Cl2 (10 mL) at -10 ˚C MsCl (1.2 mmol, 0.136 g) was added and the reaction mixture was stirred for 6 h. The reaction was quenched with H2O and extracted with CH2Cl2 (3 × 15 mL). The organic extract was washed with brine, dried over Na2SO4, and concentrated. The crude product was purified by column chromatography on silica gel (100-200 mesh), white solid, mp 119 ˚C, yield 95%; [α]D ²8 +15.7 (c 1, CHCl3). IR (neat): 3334 (br), 2964 (m), 1731 (s), 1674 (s), 1529 (m), 1361 (m), 1170 (m) cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 7.31 (s, 5 H), 6.95 (d, J = 7.5 Hz, 1 H), 5.68 (d, J = 7.2 Hz, 1 H), 5.14 (s, 2 H), 4.61-4.53 (m, 3 H), 4.35 (dd, J = 9.0, 7.2 Hz, 1 H), 3.80 (s, 3 H), 3.00 (s, 3 H), 1.93-1.84 (m, 1 H), 1.45-1.33 (m, 1 H), 1.25-1.00 (m, 1 H), 0.92-0.86 (m, 6 H). ¹³C NMR (100 MHz, CDCl3): δ = 171.7, 167.7, 155.9, 135.6, 128.54, 128.3, 128.1, 68.3, 67.5, 56.7, 53.6, 52.2, 37.6, 37.2, 24.9, 15.3, 11.4. HRMS: m/z calcd for C19H28N2O8S: 467.1467 [M + Na]; found: 467.1451.
25Compound 11 was obtained in optically pure form and there was no racemization or formation of diastereomer.