A. Rakovshik et al. / Journal of Organometallic Chemistry 706-707 (2012) 13e19
15
133.57, 133.92, 134.43, 134.72, 134.88, 137.27 (2Ph þ CH2]CH),
2.3.2. The “iodo derivative” (XV)
180.53 (CO2H). 29Si NMR (100 MHz, CDCl3) ꢀ5.29. IR (KBr):
n
2-iodo-2-diphenylmethylsilylacetic acid: Diphenyl(methyl)silyl-
acetic acid (4.29 mmol,1.10 g) was reacted with LDA (9.4 mmol) and
I2 (17.3 mmol, 2.2 gr). After standard work up procedure the crude
product contained 1.46 g of the acid and siloxane Ph2(Me)SiOSi(Me)
Ph2 as a by-product. Separation by column chromatography
resulted in decomposition of the acid (desilylation). 1H NMR
(SiCHCO2H) 1679 cmꢀ1. MS (ESI negative mode): m/z calc. for
C18H20O2Si: 296.44; found 295.07 [M ꢀ H]ꢀ.
For the preparation of XII, diphenyl(methyl)silylacetic acid
(6.75 mmol, 1.73 g) was reacted with LDA (14.8 mmol) and then
benzylbromide (7.42 mmol, 0.88 ml) was added drop-wise to the
dianion solution. The mixture was stirred overnight at room
temperature. After standard work up procedure the crude product
was crystallized from hexane to give 2.1 g (90%) of acid (XII). M.p.:
(500 MHz, CDCl3) d 0.68 (s, 3H, SiCH3), 3.72 (s, 1H, SiCHI), 7.35e7.64
(m, 10H, 2Ph), 11.59 (br, 1H, COOH).
119e121 ꢁC. 1H NMR (500 MHz, CDCl3)
d
0.72 (s, 3H, SiCH3), 2.76
2.4. A general procedure for the anodic oxidation of I, II, IV, VIeIX,
XIeXVI
(dxd, 3J ¼ 14.5 Hz, 2J ¼ 2.5 Hz,1H, SiCHCH2), 2.93 (dxd, 3J ¼ 12.0 Hz,
2J ¼ 2.5 Hz, 1H, SiCHCH2), 3.11 (dxd, 1H, 3J ¼ 12.0 Hz, 3J ¼ 14.5 Hz,
1H, SiCHCH2), 7.40 (m, 15H, 3Ph), 11.35 (br, 1H, COOH). 13C
(125 MHz, CDCl3) ꢀ5.25 (SiCH3), 33.08 (PhCH2Si), 38.32 (SiCH-
COOH), 126.14, 127.98, 128.06, 128.39, 129.87, 129.93, 133.49, 133.91,
134.74, 134.80, 134.92, 141.53 (2Ph), 179.50(COOH). 29Si NMR
The following procedure is given as a representative example
for all other oxidations: Substrate I (0.3 mmol) was electrolized in
a wall-jacketed (to allow a steady flow of tab water during elec-
trolysis) undivided cell, equipped with two carbon rods
(100 MHz, CDCl3) ꢀ5.29. IR (KBr):
n
(SiCHCOOH) 1683 cmꢀ1. HRMS
(
4
¼ 5 mm) as electrodes. The electrolyte included 3.33 mL
(ESI positive mode): m/z calc. for C22H22O2Si [M þ Na]þ: 369.1287;
a mixture of MeOH:MeCN (1:9, v/v) and 30 L of KOH solution (3 N
m
found 369.1275.
in methanol) which is equivalent to 30% of the substrate, namely
0.09 mmol. No additional electrolyte was used. Constant current
electrolysis of w30 mA/cm2 was conducted with magnetic stirring.
After the desired electricity was consumed (3 F) the solvents were
removed by evaporation and the remaining solid was dissolved in
diethyl ether and washed with 5% of aqueous sodium bicarbonate.
After phase separation the ethereal solution was dried over
magnesium sulfate and filtered. Evaporation of the ether gave
a crude mixture of products that was subjected to GCeMS and
NMR as is (or after chromatography separation on silica gel, using
hexaneeethyl acetate as eluent).
After electrolysis, a slight acidification of the aqueous phase
with HCl 2 N enabled the detection of the corresponding carboxylic
acid. For example, in the case of electrolysis of VII, cyclo-
butylcarboxylic acid was observed.
Electrolyses at Pt electrodes involved two foils (2 ꢂ 1.2 cm each),
current density of 250 mA/cm2, in MeOH:MeCN (1:3, v/v) using
0.09 mmol of KOH (3 N in methanol) for 0.3 mmol of I.
a
-Diphenyl(methyl)silylvaleric acid (XIII): Diphenyl(methyl)
silylacetic acid (4.36 mmol,1.12 g) was reacted with LDA (9.6 mmol)
and propyliodide (4.80 mmol, 0.47 ml). After standard work up
procedure the crude product was crystallized from hexane to give
1.05 g (81%) of pure acid (XIII). M.p.: 82e83 ꢁC. 1H NMR (500 MHz,
CDCl3)
d
0.67 (s, 3H, SiCH3), 0.85 (t, 3J ¼ 7.5 Hz, 3H, CH2CH2CH3) 1.28
(m, 1H, CHCH2CH2CH3), 1.42 (m, 2H, CHCH2CH2CH3), 1.84 (m, 1H,
CHCH2CH2CH3), 2.60 (dxd, 3J
¼
12.0 Hz, 3J
¼
11.5 Hz,
CHCH2CH2CH3), 7.34 (m, 6H, 2Ph), 7.56 (m, 4H, 2Ph), 11,11 (br, 1H,
CO2H). 13C (125 MHz, CDCl3) ꢀ5.34 (SiCH3), 13.61 (CH2CH3), 23.54
(CH2CH3), 29.56 (CH2CH2CH3), 36.17 (CHCO2H), 127.86, 127.93,
129.70, 129.74, 134.01, 134.35, 134.73, 134.88 (2Ph), 180.86 (CO2H).
29Si NMR (100 MHz, CDCl3) ꢀ5.76. IR (KBr):
n (SiCHCO2H)
1667 cmꢀ1 (ESI negative mode): m/z calc. for C18H22O2Si: 298.14;
found 296.78 [M ꢀ H]ꢀ.
2.3.1. The “bromo derivative” (XIV)
The procedure for the synthesis of 2ꢀbromo-2-(diphenylmethy-
silyl)acetic acid is representative for all
a
-silylcarboxylic acids of
2.5. Spectral data of major products (for minor products only
type Ph2(Me)SiCH(halogen)CO2H. Diisopropylamine (8.4 mmol,
1.2 ml) and anhydrous tetrahydrofuran (30 ml) were added to an
oven dried round-bottomed flask (100 ml) equipped with
a magnetic stirring bar. The mixture was cooled to ꢀ78 ꢁC prior of
drop-wise addition of n-butyllithium 1.6 M (8.4 mmol, 5.3 ml). The
mixture was warmed at room temperature for 15 min and cooled to
0 ꢁC. Diphenyl(methyl)silylacetic acid (3.8 mmol, 0.98 gr) in 5 ml of
dry THF was added drop-wise over 10 min to LDA solution and the
mixture was stirred for 1.5 h at the same temperature to complete
the formation of the dianion. Then CBr4 (4.2 mmol, 1.39 gr) was
added drop-wise to the dianion solution and the mixture was
stirred overnight at room temperature. The reaction mixture was
diluted by 20 ml of hexane and the organic phase washed twice
with a solution of saturated sodium chloride (2 ꢂ 30 ml) The
aqueous phase was carefully acidified with 1 N HCl to pH ¼ 2 and
then extracted with diethyl ether (20 ml ꢂ 3). The combined
organic extracts were washed with water, dried over anhydrous
MgSO4, filtered and concentrated in vacuo. The residual product
was contained 0.59gr of 2ꢀbromo-2-(diphenylmethysilyl)acetic acid
and siloxane Ph2(Me)SiOSi(Me)Ph2 as a by-product. Separation by
column chromatography resulted in decomposition of the acid
GCeMS data are reported)
Me3GeOGeMe3 (1a): GCeMS (m/z) (%): 253 (M ꢀ 1)þ, 237,145,119
(100). 1H NMR: 0.49 for ‘Me3Ge’; Me3GeOGe(Me)2OGeMe2 (1b):
GCeMS (m/z) (%): 371 (M ꢀ 1)þ, 253, 207 (100), 119. 1H NMR:
0.10e0.28 for ‘Me3GeO’ and ‘Me2GeO’ groups; Me3GeCH2CH2GeMe3
(1c): 1H NMR: 0.49 for Me3Ge; 1.43 for ‘CH2’; GCeMS (m/z) (%): 263
(Mþ), 237 (100), 119; Data for PhCH2CH2COOMe (2a) were compared
with literature [12]; 1H NMR: 3.67 for OMe 2.95 for PhCH2; 2.63 for
CH2CO2Me; GCeMS (m/z) (%): 164 (Mþ), 133, 104 (100), 91; Data for
PhCH2CH(OMe)2 (2b) were compared with literature [13]; 1H NMR:
5.23 for CH; 3.34 for OMe. GCeMS (m/z) (%): 135 (M-OMe)þ, 91, 75
(100); Me3GeCH(CH2Ph)OMe (2c), GCeMS (m/z) (%): 253 (M ꢀ 1)þ,
222, 207(100), 104. Me3GeOH (2d); GCeMS (m/z) (%): 135 (M ꢀ 1)þ,
119,104 (100). Ph2(Me)SiOH (4a): Spectral data were compared with
published data[14].1HNMR (200 MHz,CDCl3):
d
¼ 0.68(s, 3H), 2.18(s,
1H), 7.38e7.44(m, 6H), 7.59e7.64(m, 4H);13CNMR:
d
¼ ꢀ1.09,128.05,
130.03,134.49,137.19; GCeMS (m/z) (%): 214 (Mþ), 199 (100), 151, 183,
151, 121, 105; Ph2(Me)SiOCH3 (4b): Spectral datawere compared with
published data [14]. 1H NMR (200 MHz, CDCl3):
d
¼ 0.64 (s, 3H), 3.54
(s, 3H), 7.37e7.43 (m, 6H), 7.57e7.62 (m, 4H); GCeMS (m/z) (%): 228
(desilylation). IR (NaCl):
n
(C]O) 1720 cmꢀ1, 2710e3170 cmꢀ1
0.60 (s, 3H, SiCH3), 3.90 (s,
(Mþ), 213(100),183,151,121,105;Ph2(Me)SiOSi(Me)Ph2 (4c):Spectral
(COOH). 1H NMR (500 MHz, CDCl3)
d
data were compared with published data [14]. 1H NMR:
d
¼ 0.59 (s,
1H, SiCHBr), 7.32e7.55 (m, 10H, 2Ph), 11.35 (br, 1H, CO2H); 13C
(125 MHz, CDCl3) ꢀ0.60 (SiCH3), 32.34 (BrCHSi), 127.70, 129.55,
133.97, 137.43, (2Ph), 167.52 (CO2H).
6H), 7.29e7.40 (m, 6H), 7.51e7.56 (m, 4H);13C NMR:
d
¼ ꢀ0.43,127.87,
129.71,134.14,137.72;GCeMS(m/z) (%): 410 (Mþ), 395 (100), 317, 255,
195, 151; Ph2(Me)SiGeMe3 (4d);GCeMS (m/z)(%):315 (Mꢀ 1)þ (100),