2-(Trimethylsilyl)-1,3-dithiane 1-oxide as a convenient reagent for the transformation of aldehydes and ketones into homologous carboxylic acids

Article abstract of DOI:10.1055/s-0029-1218820

Aldehydes and ketones were converted into the corresponding homologous carboxylic acids in two steps by treatment with 2-(trimethylsilyl)-1,3-dithiane 1-oxide. A modified Peterson olefination of the carbonyl compounds gave ketene thioacetal sulfoxides that were readily cleaved in acidic acetonitrile to give the required carboxylic acids. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0029-1218820

2616
PAPER
2-(Trimethylsilyl)-1,3-dithiane 1-Oxide as a Convenient Reagent for the
Transformation of Aldehydes and Ketones into Homologous Carboxylic Acids
Homologation of
A
a
ldehydes
a
r
nd Keto
s
ne
s
to Ca
r
t
boxylic
e
Acids n Krohn,* Stephan Cludius-Brandt
Department Chemie, Universität Paderborn, Warburger Str. 100, 33098 Paderborn, Germany
Fax +49(5251)603245; E-mail: k.krohn@uni-paderborn.de
Received 14 February 2010; revised 9 April 2010
We therefore looked for a more general and more easily
Abstract: Aldehydes and ketones were converted into the corre-
sponding homologous carboxylic acids in two steps by treatment
with 2-(trimethylsilyl)-1,3-dithiane 1-oxide. A modified Peterson
olefination of the carbonyl compounds gave ketene thioacetal sulf-
obtainable reagent, and preferably one that is available
commercially. After some experimentation, we found that
2-(trimethylsilyl)-1,3-dithiane ideally fulfilled our re-
oxides that were readily cleaved in acidic acetonitrile to give the re- quirements because it is commercially available and it can
quired carboxylic acids.
be oxidized nearly quantitatively in one step by sodium
metaperiodate or tert-butyl hydroperoxide to give the cor-
responding 1-oxide. The oxide reagent can also be readily
prepared by addition of lithiated 1,3-dithiane to trimethyl-
silyl chloride9 and subsequent oxidation by sodium meta-
periodate.10 Oxidation is not required for the addition
reaction of the dithiane with carbonyl compounds, but it is
needed to facilitate the subsequent cleavage of the dithio-
acetals to give carboxylic compounds.8 In addition, the re-
quired elimination step to give the intermediate ketene
acetal (see Scheme 1) is facilitated when a modified
Peterson olefination procedure is used.
Key words: aldehydes, ketones, carboxylic acids, homologation
One-carbon homologation reactions of aldehydes, ke-
tones, or carboxylic acids are important transformations in
organic synthesis, and many different strategies for these
transformations have been developed in recent decades.1
This one-carbon transfer does not follow mainstream eno-
late chemistry,2 and in many cases umpolung reagents are
used.3 Aldehyde-to-acid homologation is possible by the
addition of an appropriate dithio-substituted nucleophile
and subsequent hydrolysis. Indeed, an increase in oxida-
tion state to the corresponding acid was observed during
our work on the acid-catalyzed rearrangement reactions of
a-hydroxy-1,3-dithianes and a-hydroxy-1,3-dithiane 1-
oxides (Scheme 1).4a The intermediate ketene dithioace-
tals, such as A, are assumed to act as intermediates.4b De-
pending on the hydrolysis conditions, an ester,5 thioester,6
or carboxylic acid7 can be isolated. Similarly, methyl
(methylsulfanyl)methyl sulfoxide can be used in the trans-
formation of substituted benzaldehydes into the corre-
sponding phenylacetic acids.4b–g However, the synthesis
of this reagent required a somewhat tedious multistep pro-
cedure, and its action is restricted to the transformation of
aromatic aldehydes.4b
We now wish to report on this method, which permits the
synthesis of the homologous aromatic or aliphatic carbox-
ylic acids from the corresponding aldehydes or ketones in
a simple two-step process.
The general route for the homologation of the carbonyl
compound 1 involves the formation of an intermediate
ketene acetal (2) and its subsequent hydrolysis to the acid
3 (Scheme 2).
R1
R1
R1
S
S
O
S
O
Me3Si
O
R2
. R2
O
R2
OH
S
1
2
3
O
OH
O
S
R1 = H, alkyl
2 = alkyl, alkenyl, aryl, aralkyl
R1–R2 = cycloalkyl
S
H+, MeCN
R
S
S
Scheme 2 Homologation of carbonyl compounds to carboxylic
acids
A
H2O, H+
O
S
S
+
OH
To explore the scope and limitations of the new reagent,
we selected a number of aromatic, aliphatic, and unsatur-
ated aldehydes and ketones with various degrees of steric
hindrance (1a–j). These were readily converted into the
required ketene dithioacetals 2a–j by Peterson olefination
with 2-(trimethylsilyl)-1,3-dithiane 1-oxide (Table 1).
Subsequently, treatment of the ketene dithioacetals 2a–j
with excess 6 M hydrochloric acid in acetonitrile with
warming to 55–65 °C until the starting material was com-
1,2-dithiolane
Scheme 1 Formation of a carboxylic acid from an a-hydroxy-1,3-
dithiane 1-oxide4b
SYNTHESIS 2010, No. 15, pp 2616–2620
Advanced online publication: 17.06.2010
DOI: 10.1055/s-0029-1218820; Art ID: T03610SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
1
0

PAPER
Homologation of Aldehydes and Ketones to Carboxylic Acids
2617
Table 1 Formation of Ketene Dithioacetals 2 and Their Conversion into Carboxylic Acids 3
Ketene dithioacetal
Yield (%)
76
Time (h)
2
Acid
Yield (%)
85
O
S
O
O
2a
3a
OH
S
O
S
2b
2c
2d
79
70
75
7
7
6
3b
3c
3d
94
88
91
OH
OH
OH
S
O
S
O
O
S
O
S
S
S
O
OH
S
2e
70
2.5
3e
92
O
O
MeO
MeO
O
MeO
S
2f
75
65
5
2
3f
85
40
OH
S
MeO
O
O
O
O
S
2g
3g
OH
OH
S
S
S
2h
69
3
3h
71
O
O
S
2i
55
51
6
3i
3j
92
90
OH
S
O
OH
S
2j
11
O
S
pletely consumed (thin-layer chromatography) gave the
corresponding carboxylic acids 3a–j in good-to-very
good yields, with exception of the olefinic ketene acetal
2g; in this case, side reactions of the double bond probably
occurred in the acidic medium.
H+
R2
O
S
R2
H+
OH OH2
S
H+
R1
H
R1
H
S
S
O
O
2
H
H
Scheme 3 shows the presumed mechanism for the cleav-
age of the ketene dithioacetals 2a–j.
R2
O
C
S
O
S
R1
R1
Addition of a proton to the oxygen atom of the sulfoxide
and attack by water led to the formation of the ketene and
1,2-dithiolane, which could be detected in the crude reac-
tion mixture by NMR spectroscopy (see also Ogura and
Tsuchihashi4b). Because excess water was present in the
+
R2
OH
3
R1 = alkyl, aryl; R2 = Me, H
Scheme 3 Mechanism for the cleavage of ketene dithioacetals 2a–j
Synthesis 2010, No. 15, 2616–2620 © Thieme Stuttgart · New York

2618
K. Krohn, S. Cludius-Brandt
PAPER
1H NMR (500 MHz, CDCl3): d = 2.31–2.92 (m, 5 H), 3.26–3.41 (m,
1 H), 7.40–7.49 (m, 2 H), 7.62 (s, 1 H), 7.71–7.85 (m, 3 H), 7.88–
7.97 (m, 1 H), 8.12 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 27.4, 32.2, 55.4, 126.9, 127.4,
127.5, 128.0, 128.3, 128.9, 130.8, 131.6, 133.4, 133.7, 134.7, 137.5.
MS (EI): m/z (%) = 274 (30) [M]+, 171 (57), 141 (16), 106 (20), 90
(23), 57 (20).
acidic solution, the ketene was transformed directly into
the corresponding carboxylic acid.
In summary, we have shown that aromatic or aliphatic al-
dehydes and ketones can be readily converted into the cor-
responding homologous carboxylic acids by treatment
with 2-(trimethylsilyl)-1,3-dithiane 1-oxide, with subse-
quent acidic cleavage of the 1,3-dithiane 1-oxide moiety
in acetonitrile.
HRMS: m/z calcd for C15H14OS2: 274.04832; found: 274.05011.
Anal. Calcd for C15H14OS2: C, 65.68; H, 5.14; S, 23.33. Found: C,
63.97; H, 5.11; S, 22.39.
Column chromatography was performed on silica gel 60 (particle
size 0.040–0.063 mm). NMR spectra were recorded on a Bruker
ARX 200 or ARX 500 instrument at r.t. Chemical shifts are given
in ppm relative to TMS. Mass spectra were recorded on Finnegan
MAT 8200 and Fison MD 800 instruments. Solvents were purified,
if necessary, by standard methods.
2-(3-Phenylpropylidene)-1,3-dithiane 1-Oxide (2d)
Yield: 75%.
1H NMR (200 MHz, CDCl3): d = 2.18–3.06 (m, 9 H), 3.14–3.32 (m,
1 H), 6.73 (t, J = 7.0 Hz, 1 H), 7.14–7.37 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 27.3, 30.7, 31.7, 35.2, 55.2, 126.5,
128.7, 129.2, 137.9, 138.0, 141.0.
MS (EI): m/z (%) = 252 (19) [M]+, 235 (14), 209 (53), 177 (50), 145
(42), 129 (53), 106 (36), 91 (45), 73 (100), 41 (28).
Oxidation of 2-(Trimethylsilyl)-1,3-dithiane by Sodium Meta-
periodate
A soln of NaIO4 (3.5 g, 16.6 mmol) in H2O (20 mL) was added to
2-(trimethylsilyl)-1,3-dithiane (3.2 g, 16.6 mmol) in MeOH
(150 mL) while the temperature was kept below 10 °C. After 4 h at
0–6 °C, the soln was allowed to warm to r.t. and filtered. The sol-
vent was removed from the filtrate and the residue was partitioned
between brine and CHCl3 then dried (Na2SO4) and concentrated to
give a light yellow oil; yield: 3.1 g (90%).
HRMS: m/z calcd for C13H16OS2: 252.06425; found: 252.06074.
Anal. Calcd for C13H16OS2: C, 61.88; H, 6.39; S, 25.36. Found: C,
60.62; H, 6.75; S, 25.46.
2-(2-Phenylethylidene)-1,3-dithiane 1-Oxide (2e)
Yield: 70%.
Ketene Dithioacetals 2a–j; General Procedure
1H NMR (200 MHz, CDCl3): d = 2.32–2.88 (m, 5 H), 3.27–3.43 (m,
1 H), 3.84 (d, J = 7.5 Hz, 2 H), 6.89 (t, J = 7.7 Hz, 1 H), 7.19–7.35
(m, 5 H).
13C NMR (50 MHz, CDCl3): d = 27.3, 31.9, 35.3, 55.2, 126.9,
128.9, 129.1, 137.5, 138.0, 138.7.
MS (EI): m/z (%) = 238 (61) [M]+, 221 (71), 147 (69), 115 (74), 106
(69), 91 (85), 84 (88), 49 (100).
A soln of 2-(trimethylsilyl)-1,3-dithiane 1-oxide (1.04 g, 5 mmol)
in THF (20 mL) was cooled to –78 °C and a 2.5 M soln of BuLi in
hexane (2.08 mL, 5.2 mmol) was added over 10 min. The soln was
allowed to warm to 0 °C during 1.5 h and then cooled to –78 °C. A
soln of a carbonyl compound 1a–j (5 mmol) in THF was added over
10 min, and the soln was warmed to r.t. and left overnight. The soln
was poured into sat. aq NH4Cl (100 mL) and extracted with EtOAc
(3 × 50 mL). The extracts were dried (Na2SO4) and concentrated
under reduced pressure, and the resulting crude product was puri-
fied by column chromatography [silica gel, CH2Cl2–MeOH (1%)].
HRMS: m/z calcd for C12H14OS2: 238.0486; found: 238.04774.
2-(3,4-Dimethoxybenzylidene)-1,3-dithiane 1-Oxide (2f)
Yield: 75%.
2-[(2E)-3-Phenylprop-2-en-1-ylidene]-1,3-dithiane 1-Oxide (2a)
1H NMR (200 MHz, CDCl3): d = 2.46–2.92 (m, 5 H), 3.35–3.40 (m,
1 H), 3.88 (s, 3 H), 3.90 (s, 3 H), 6.87 (d, J = 8.3 Hz, 1 H), 7.33 (d,
J = 8.3 Hz, 1 H), 7.38 (s, 1 H), 7.50 (s, 1 H).
Yield: 76%.
1H NMR (200 MHz, CDCl3): d = 2.41–3.01 (m, 5 H), 3.35–3.49 (m,
1 H), 6.95 (d, J = 14.4 Hz, 1 H), 7.26–7.60 (m, 7 H).
13C NMR (50 MHz, CDCl3): d = 27.0, 31.8, 55.0, 55.9, 110.8,
112.8, 124.2, 126.7, 133.6, 134.2, 148.6, 149.9.
13C NMR (50 MHz, CDCl3): d = 27.1, 31.6, 55.0, 122.2, 127.2,
128.7, 128.8, 135.3, 136.3, 137.0, 138.9.
MS (EI): m/z (%) = 284 (48) [M]+, 178 (85), 168 (100), 149 (68), 97
(31), 71 (41), 57 (59).
MS (EI): m/z (%) = 250 (40) [M]+, 160 (30), 144 (100), 128 (65),
123 (90), 115 (50), 106 (20), 91 (73).
HRMS: m/z calcd for C13H16OS2: 284.05387; found: 284.05299.
HRMS: m/z calcd for C13H14OS2: 250.04879; found: 250.04485.
Anal. Calcd for C13H16O3S2: C, 54.91; H, 5.67; S, 22.51. Found: C,
53.90; H, 5.55; S, 23.31.
2-Benzylidene-1,3-dithiane 1-Oxide (2b)
Yield: 79%.
1H NMR (500 MHz, CDCl3): d = 2.47–2.67 (m, 3 H), 2.81–2.91 (m,
2 H), 3.39–3.45 (m, 1 H), 7.33–7.45 (m, 3 H), 7.52 (s, 1 H), 7.74–
7.78 (m, 2 H).
2-[(2E)-1-Methyl-3-phenylprop-2-en-1-ylidene]-1,3-dithiane 1-
Oxide (2g)
Yield: 65%.
1H NMR (200 MHz, CDCl3): d = 2.37 (s, 3 H), 2.61–3.06 (m, 5 H),
3.17–3.37 (m, 1 H), 6.90 (d, J = 15.4 Hz, 1 H), 7.33–7.55 (m, 5 H),
7.85 (d, J = 15.4 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 16.4, 17.9, 31.1, 48.6, 124.1,
127.4, 129.1, 129.2, 134.2, 135.9, 136.8, 146.4.
13C NMR (125 MHz, CDCl3): d = 27.4, 32.2, 55.3, 128.9, 129.6,
130.6, 134.1, 134.7, 137.2.
Anal. Calcd for C11H12OS2: C, 58.91; H, 5.39; S, 28.54. Found: C,
58.66; H, 5.40; S, 28.26.
MS (EI): m/z (%) = 264 (12) [M]+, 174 (27), 158 (90), 149 (49), 106
(25), 83 (89), 48 (100).
2-(2-Naphthylmethylene)-1,3-dithiane 1-Oxide (2c)
Yield: 70%.
HRMS: m/z calcd for C14H16OS2: 264.06425; found: 264.06234.
Synthesis 2010, No. 15, 2616–2620 © Thieme Stuttgart · New York

PAPER
Homologation of Aldehydes and Ketones to Carboxylic Acids
2619
2-(4-Phenylcyclohexylidene)-1,3-dithiane 1-Oxide (2h)
Yield: 69%.
13C NMR (50 MHz, CDCl3): d = 41.5, 127.7, 129.0, 129.8, 133.7,
178.1.
1H NMR (200 MHz, CDCl3): d = 1.49–1.81 (m, 4 H), 1.83–2.19 (m,
2-Naphthylacetic Acid (3c)
Yield: 88%.
1H NMR (200 MHz, CDCl3): d = 3.85 (s, 2 H), 7.38–7.92 (m, 7 H),
10.61 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 41.6, 126.4, 126.7, 127.8, 128.1,
128.6, 128.7, 131.3, 132.9, 133.8, 178.0.
4 H), 2.58–2.98 (m, 6 H), 3.08–3.19 (m, 1 H), 7.12–7.34 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 15.7, 30.7, 31.6, 33.4, 34.8, 35.0,
44.4, 48.6, 126.3, 126.7, 128.5, 129.1, 145.4, 155.1.
MS (EI): m/z (%) = 292 (6) [M]+, 275 (77), 209 (38), 177 (36), 106
(30), 91 (30), 73 (100), 41 (30).
HRMS: m/z calcd for C16H20OS2: 292.09555; found: 292.09363.
4-Phenylbutanoic Acid (3d)
Yield: 91%.
Anal. Calcd for C16H20OS2: C, 65.75; H, 6.90; S, 21.89. Found: C,
64.95; H, 6.82; S, 21.75.
1H NMR (200 MHz, CDCl3): d = 1.87–1.94 (m, 2 H), 2.31 (t,
J = 7.4 Hz, 2 H), 2.61 (t, J = 7.7 Hz, 2 H), 7.09–7.23 (m, 5 H), 11.65
(br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 26.3, 33.2, 35.1, 126.0, 128.4,
128.5, 141.2, 178.4.
2-Hexylidene-1,3-dithiane 1-Oxide (2i)
Yield: 55%.
1H NMR (200 MHz, CDCl3): d = 0.85 (t, J = 6.5 Hz, 3 H), 1.14–
1.51 (m, 6 H), 2.26–3.15 (m, 7 H), 3.19–3.33 (m, 1 H), 6.43 (t,
J = 7.8 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 14.3, 22.7, 27.2, 28.6, 29.0, 31.6,
31.8, 55.1, 136.7, 145.2.
3-Phenylpropanoic Acid (3e)
Yield: 92%.
1H NMR (200 MHz, CDCl3): d = 2.69 (t, J = 8 Hz, 2 H), 2.97 (t,
J = 8 Hz, 2 H), 7.19–7.33 (m, 5 H), 10.77 (br s, 1 H).
MS (EI): m/z (%) = 218 (10) [M]+, 201 (15), 163 (27), 131 (44), 113
(78), 106 (39), 84 (97), 55 (86), 43 (100).
13C NMR (50 MHz, CDCl3): d = 30.8, 35.7, 126.4, 128.2, 128.5,
140.2, 178.9.
HRMS: m/z calcd for C10H18OS2: 218.0799; found: 218.07815.
2-(2-Methylpropylidene)-1,3-dithiane 1-Oxide (2j)
Yield: 51%.
1H NMR (200 MHz, CDCl3): d = 1.04 (d, J = 6.8 Hz, 3 H), 1.09 (d,
J = 6.8 Hz, 3 H), 2.28–2.81 (m, 6 H), 3.01–3.22 (m, 1 H), 6.52 (d,
J = 9.6 Hz, 1 H).
(3,4-Dimethoxyphenyl)acetic Acid (3f)
Yield: 85%.
1H NMR (200 MHz, CDCl3): d = 3.69 (s, 2 H), 3.89 (s, 3 H), 3.90
(s, 3 H), 6.85–7.09 (m, 3 H).
13C NMR (50 MHz, CDCl3): d = 40.6, 55.7, 55.9, 111.5, 112.6,
121.6, 125.7, 148.7, 150.3, 177.8.
13C NMR (50 MHz, CDCl3): d = 22.6, 22.7, 27.4, 28.8, 32.0, 55.2,
134.8, 145.9.
MS (EI): m/z (%) = 190 (20) [M]+, 173 (58), 159 (14), 106 (35), 85
(40), 60 (100).
2-Methyl-4-phenylbut-3-enoic Acid (3g)
Yield: 40%.
HRMS: m/z calcd for C8H14OS2: 190.0486; found: 190.04716.
1H NMR (200 MHz, CDCl3): d = 1.42 (d, J = 7.1 Hz, 3 H), 3.36 (m,
1 H), 6.28 (dd, J = 15.9 Hz, 7.7 Hz, 1 H), 6.52 (d, J = 15.9 Hz, 1 H),
7.28–7.42 (m, 5 H).
Carboxylic Acids 3a–3j; General Procedure
A soln of ketene dithioacetal 1-oxide 2a–j (1 mmol) in MeCN
(10 mL) was treated with 6 M aq HCl (1.5 mmol, 0.25 mL), and the
soln was warmed to 55–65 °C until the starting material was con-
sumed (TLC). When the reaction was complete, the soln was
poured into H2O (20 mL) and extracted with CH2Cl2 (3 × 10 mL).
The combined organic layer was washed with brine (20 mL), dried
(Na2SO4), and concentrated to give a crude product that was puri-
fied, if necessary, by column chromatography (silica gel, PE–
EtOAc).
13C NMR (50 MHz, CDCl3): d = 17.2, 40.1, 126.3, 127.6, 128.0,
128.3, 131.7, 136.7, 181.1.
4-Phenylcyclohexanecarboxylic Acid (3h)
Yield: 71%.
1H NMR (200 MHz, CDCl3): d = 1.45–1.67 (m, 4 H), 2.07–2.19 (m,
4 H), 2.48–2.57 (m, 1 H), 2.71–2.82 (m, 1 H), 7.15–7.39 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 29.1, 33.2, 42.7, 43.5, 126.1,
126.7, 128.3, 146.7, 181.0.
4-Phenylbut-3-enoic Acid (3a)
Yield: 85%.
Heptanoic Acid (3i)
Yield: 92%.
1H NMR (200 MHz, CDCl3): d = 0.91 (t, J = 6.3 Hz, 3 H), 1.23–
1.70 (m, 8 H), 2.37 (m, 2 H), 10.40 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 14.4, 22.9, 25.0, 29.1, 31.8, 34.5,
180.9.
1H NMR (200 MHz, CDCl3): d = 3.35 (d, J = 6.9 Hz, 2 H), 6.24–
6.44 (m, 1 H), 6.58 (d, J = 16 Hz, 1 H), 7.26–7.49 (m, 5 H), 10.57
(br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 38.4, 121.3, 126.7, 128.2, 129.0,
134.4, 137.1, 178.5.
Phenylacetic Acid (3b)
Yield: 94%.
1H NMR (200 MHz, CDCl3): d = 3.69 (s, 2 H), 7.21–7.45 (m, 5 H),
11.01 (br s, 1 H).
3-Methylbutanoic Acid (3j)
Yield: 90%.
1H NMR (200 MHz, CDCl3): d = 0.98 (d, J = 6.6 Hz, 6 H), 2.08–
2.12 (m, 1 H), 2.23 (d, J = 7.2 Hz, 2 H), 10.79 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 22.3, 25.4, 43.0, 178.5.
Synthesis 2010, No. 15, 2616–2620 © Thieme Stuttgart · New York

2620
K. Krohn, S. Cludius-Brandt
PAPER
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