F. Bickelhaupt, M. Newcomb, C. B. DeZutter, H. J. R. de Boer
FULL PAPER
1.5 Hz, 1 H) ppm. 13C NMR: δ = 43.9, 55.9, 112.4, 126.7, 128.1,
129.2, 133.5, 137.2, 137.5, 145.7, 166.3. 175.8 ppm.
and solvent attack can be neglected. The rate constant for
phenyl migration in the 2,2,2-triphenylethyl radical 8 is de-
scribed by logk = 11.2 – 7.5/2.3 RT [kcal/mol], and the rate
constant for rearrangement at 20 °C is 4.0ϫ105 s–1.The (ex-
tended) diffusion model for Grignard reagent formation re-
actions is consistent with our experimental results. During
the reaction, a dark-red solution is formed which may be
indicative for the intermediate formation of a carbanionic
species.
Kinetic Studies: The laser flash photolysis method was the same as
described previously.[16,21] Thus, THF solutions containing PTOC
ester 10 in a thermostatted addition funnel were purged with he-
lium to remove oxygen. The solutions were allowed to flow through
a reaction cell and were irradiated with 355 nm laser light, and the
reaction was monitored at varying wavelengths. The individual runs
were collected to generate the time-resolved UV/Vis spectrum of
the reaction shown in Figure 1. Kinetics were determined by fitting
the growth of signal at ca. 335 nm to a single exponential growth
function.
Experimental Section
2-Chloro-1,1,1-triphenylethane (1): Compound 1 was prepared from
triphenylmethylsodium and dichloromethane according literature
procedures.[7a] After crystallisation from hexane, white crystals of
1 were obtained in 51% yield (35%[7a]). M.p. 99 °C (101 °C[7a]). 1H
NMR (90 MHz, CDCl3, 25 °C): δ = 4.64 (s, 2 H, CH2), 7.05–7.23
(m, 15 H, arom.) ppm. MS: m/z (%) = 292 (1) [M+], 256 (22), 243
(100), 178 (13), 165 (50).
Acknowledgments
This work was supported in part by a grant from the National
Science Foundation (CHE-0601857) to M. N.
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Reaction of 1 with Mg in THF: A mixture of 1 (500 mg, 1.7 mmol),
triply sublimed Mg (410 mg, 17.1 mmol) and THF (10 mL) was
vigorously stirred at room temperature for 24 h, whereafter a dark-
red solution was obtained. On addition of D2O, the dark-red col-
our disappeared immediately, whereupon a saturated aqueous solu-
tion of ammonium chloride and Et2O were added. The organic
fraction was separated, and the aqueous fraction was extracted
with Et2O. The organic fractions were combined, washed with
water and dried with anhydrous MgSO4. The solvent was evapo-
rated leaving a white solid (445 mg). The product distribution was
1
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determined by H NMR analysis (250 MHz, CDCl3, 25 °C, pulse
delay 15 s). Compound 4 was separated from 2 and 3 by prepara-
tive GLC: 1,1,1-Triphenylethane (2). Yield: 16%. 1H NMR
(250 MHz, CDCl3, 25 °C): δ = 2.17 (s, 3 H, CH3), 7.05–7.08 (m, 6
H, arom.), 7.19–7.24 (m, 9 H, arom.) ppm. MS: m/z (%) = 258 (11)
[M+], 243 (100), 165 (30).[30] 2-D-1,1,1-triphenylethane (3). Yield:
52%. 1H NMR (250 MHz, CDCl3, 25 °C): δ = 2.15 (br. s, ν1/2
=
4 Hz, 2 HCH2), 7.05–7.08 (m, 6 H, arom.), 7.19–7.24 (m, 9 H,
arom.) ppm. MS: m/z (%) = 259 (11) [M+], 243 (100), 165 (39).
Triphenylethene (4). Yield: 26%. 1H NMR (250 MHz, CDCl3,
25 °C): δ = 6.88 (br. s, 1 H, CH), 6.91–6.96 (m, 2 H, arom.), 6.99–
7.06 (m, 3 H, arom.), 7.09–7.16 (m, 2 H, arom.), 7.19–7.28 (m, 8
H, arom.) ppm. MS: m/z (%) = 256 (100) [M+], 241 (22), 240 (14),
239 (23), 179 (24), 178 (40), 165 (13).[31] This experiment was re-
peated in completely sealed and evacuated glass apparatus, wherein
the dark-red solution was also formed and remained even after
months. Samples were taken and analysed by 1H NMR spec-
troscopy and GC-MS after 29 h, 53 h and 175 h. However, the
product distribution of all samples was identical within experimen-
tal error.
1-[(3,3,3-Triphenylpropanoyl)oxy]pyridine-2(1H)-thione (10): 1-Hy-
droxy-1H-pyridine-2-thione (0.51 g, 4.00 mmol) and 1,3-dicyclo-
hexylcarbodiimide (0.83 g, 4.00 mmol) were dissolved in dichloro-
methane (50 mL). The flask was shielded from light, and 3,3,3-
triphenylpropionic acid (1.10 g, 3.64 mmol) was added. The mix-
ture was stirred for 2.5 h, after which it was washed sequentially
with 10% NaHCO3 solution and brine. Drying with Na2SO4, sol-
vent removal by rotary evaporation, and chromatography on silica
gel (3:1, hexanes/ethyl acetate) provided the PTOC ester as a light
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1
yellow solid (1.11 g, 74%). H NMR: δ = 4.16 (s, 2 H), 6.42 (td, J
= 6.5, 1.5 Hz, 1 H), 6.60 (dd, J = 7.0, 1.0 Hz, 1 H), 7.09 (td, J =
6.5, 1.5 Hz, 1 H), 7.24 (m, 4 H), 7.29 (m, 11 H), 7.61 (dd, J = 8.5,
6230
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