R. Knorr et al. / Journal of Organometallic Chemistry 824 (2016) 61e72
71
(entry 2); for 13C NMR, see Table 4. Anal. calcd for
15H21LiOþ0.95LiBr (306.8): C, 58.72; H, 6.90; combustion residue,
4.7. a,b-Dibromo-2-isopropylstyrene (9)
C
31.8. Found: C, 58.58; H, 7.01; combustion residue, 31.7.
The procedure of preparing this material in an NMR tube is
described for [6-D]5 in the Supplementary Data. Unfortunately, our
attempts to recrystallize 22 or to find a suitable single crystal for an
X-ray structural analysis were unsuccessful, so that we cannot
differentiate between a conglomerate and a mixed crystal of
5&Et2O with LiBr. Nevertheless, 22 served well to obtain purified
samples of solvated 5.
2-Isopropylstyrene (8, 8.93 g, 6.11 mmol) in chloroform (50 mL)
was stirred during the dropwise addition of elemental bromine
(3.12 mL, 9.80 g, 6.13 mmol) in chloroform (10 mL). After 1 h at r.t.,
evaporation of most of the solvent afforded 9 as a crude oil (20.3 g);
1H NMR (CCl4, 60 MHz)
d
1.29 (d, 3J ¼ 6.8 Hz, ca. 6H, 2 ꢄ CH3), 3.28
(sept, 3J ¼ 6.8 Hz, 1H, isopropyl-H), 4.07 (AB part of ABX system,
apparent doublet with 3J ¼ 8.0 Hz, 2H, CH2Br), 5.55 (X part,
apparent triplet with 3J ¼ 8.0 Hz, CHBr), 7.25 (m, 4H, C6H4) ppm.
4.4.2. By Sn/Li interchange: LiBr-free 5
4.8. (2-Isopropylphenyl)acetylene (10)
Crude
3-(tributylstannyl)-1,1-dimethylindene
(407
mg,
<0.9 mmol since consisting of only 63% of 25 along with other
butylstannyl compounds [11]) was dissolved in anhydrous t-
BuOMe (0.40 mL) and titrated with n-Bu6Li (ca. 0.6 mmol) in
cyclopentane (0.28 mL) for the total consumption of 25 (t1/2 ¼ ca.
20 min). On addition of [D12]cyclohexane (0.10 mL) and a trace of
TMS, the clear solution produced no precipitate. After the first se-
ries of NMR measurements, 0.33 mL of this solution were diluted
with anhydrous t-BuOMe (0.33 mL) and measured again; this led to
A three-necked, round-bottomed flask (500 mL) was charged
with a suspension (45 g) of NaNH2 in toluene, dry THF (100 mL),
and a magnetic stirring bar, then fitted with a pressure-equalizing
dropping funnel and a reflux condenser carrying a gas bubbler
with inlet and outlet for slowly streaming, dry N2 gas. (A less
enormous excess of NaNH2 may also work well, but the stoichio-
metric minimum is 3 equiv.) A solution of the crude dibromide 9
(52.4 mmol) in anhydrous Et2O (50 mL) was added dropwise with
stirring, whereupon the mixture was refluxed overnight. The
generated sodium acetylide and remnant NaNH2 in the cooled and
stirred mixture were quenched through the cautious, dropwise
introduction of saturated aqueous NH4Cl until the gas evolution
ceased. After acidification with half-concentrated HCl, the aqueous
layer was separated and extracted with Et2O (3ꢄ). The Et2O extracts
were combined with the organic layer, washed with distilled water
until neutral, dried over MgSO4, and concentrated. The alkyne 10
distilled at 75e76 ꢁC/14 Torr and was contaminated with some
toluene (0.19 equiv): Corrected yield 5.77 g (76%); 1H NMR (CCl4,
the observation of a13C-
Table 5).
a
quintet pattern at ꢀ95 ꢁC (entry 12 of
4.5. 1-(2-Isopropylphenyl)ethanol (7)
The solution of O]CHeCH3 (15.0 g, 341 mmol) in anhydrous
Et2O (150 mL) was added dropwise to the Grignard reagent 6 that
had been prepared from 1-bromo-2-isopropylbenzene (60.0 g,
302 mmol) and Mg turnings (7.40 g, 304 mmol) in Et2O (130 mL).
The mixture was refluxed for 60 min, cooled, and worked up with
aqueous NH4Cl, HCl (2 M), and Et2O. The washed and dried Et2O
extracts were concentrated and purified by fractionating distilla-
tion: Yield 17.0 g (34%), bp 117e118 ꢁC/12 Torr; 1H NMR (CCl4,
60 MHz)
d
1.26 (d, 3J ¼ 7.0 Hz, ca. 6H, 2 ꢄ CH3), 3.11 (s, 1H, alkynyl-
H), 3.51 (sept, 3J ¼ 7.0 Hz, 1H, tert. isopropyl-H), 7.20 (broad m, ca.
4H, C6H4) ppm. Redistillations afforded analytically pure 10: IR
60 MHz)
d
1.20 (d, 3J ¼ 6.8 Hz, ca. 6H, 2 ꢄ CH3), 1.35 (d, 3J ¼ 6.3 Hz,
(film) n 3298 (s, ≡CeH), 3090, 3065, 3022, 2960 (s), 2925, 2872
ca. 3H, CH3), 2.71 (s, 1H, OH), 3.22 (sept, 3J ¼ 6.8 Hz, 1H, tert.
(sharp CeH), 2101 (w, C^C),1481 (s),1445, 757 (s) cmꢀ1. Anal. calcd
for C11H12 (144.2): C, 91.61; H, 8.39. Found: C, 91.42; H, 8.65.
The alternative methods of replacing NaNH2 by the KOCMe3/
HOCMe3 complex (exothermic) or by distillation of 9 over solid
KOH required enhanced temperatures for the final dehydrobromi-
3
isopropyl-H), 5.10 (q, J ¼ 6.3 Hz, 1H, CHeO), ca. 7.15 (broad m, ca.
4H, C6H4) ppm; IR (film)
n 3600e3100 (broad, OeH), 2962, 2925,
2868, 1486, 1447, 1383, 1364, 1069 (s), 1002, 755 (s) cmꢀ1. Anal.
calcd for C11H16O (164.2): C, 80.44; H, 9.82. Found: C, 80.01; H, 9.74.
nation of the unwelcome primary product
b-bromo-2-
4.6. 2-Isopropylstyrene (8)
isopropylstyrene. This unknown b-bromide was not purified but
recognized by its 1H NMR data in CCl4:
d
1.22 (d, 3J ¼ 6.8 Hz,
A round-bottomed flask (50 mL) was charged with the alcohol 7
(16.6 g, 101 mmol) and annealed KHSO4 (2.5 g), then fitted to a
distillation bridge with an ice-cooled receptacle. Under a contin-
uous pressure of 11 Torr, the flask was heated first at 100 ꢁC and
then up to 200 ꢁC in the course of 3 h. The distillate (13.7 g) was
diluted with Et2O and dried over MgSO4, then distilled again to give
the pure olefin 8. Yield 7.12 g (49%); bp 78e81 ꢁC/11 Torr; 1H NMR
2 ꢄ CH3), 3.15 (sept, 3J ¼ 6.8 Hz, tert. isopropyl-H), 6.48 and 7.18 (AB
system, 3J ¼ 13.8 Hz,
a-H and b-H) ppm.
4.9.
a-Bromo-2-isopropylstyrene (11)
The alkyne 10 (2.76 g, 19.1 mmol) in glacial acetic acid (20 mL)
was stirred in an Erlenmeyer flask (100 mL) and saturated with
solid NaBr (<3 g). Concentrated aqueous HBr (47%, 6.0 mL) was
decolorized with a few small Na2SO3 crystals, then added dropwise
to the flask. After stirring for 30 min at r.t., the flask was heated on a
steam bath for 30 min, cooled, and emptied into distilled water
(100 mL). The mixture was extracted with Et2O (3 ꢄ 50 mL), and the
combined extracts were shaken with aqueous NaOH (2 M) until
alkaline, washed with water until neutral, dried over Na2SO4, and
concentrated to give a mixture of 11 with 2-isopropylacetophenone
(4:1, 4.24 g). This mixture was dissolved in a small amount of CCl4,
then adsorbed on a small column of Al2O3, and eluted with CCl4
(200 mL). The first fraction contained 11 only and distilled at
100e120 ꢁC (bath temp.)/12 Torr to furnish practically pure 11 that
could not be obtained in an analytically pure state: Yield 3.50 g
(CDCl3, 60 and 100 MHz): Table 1; 1H NMR (CCl4, 60 MHz)
d 1.22 (d,
3J ¼ 6.8 Hz, 6H, 2 ꢄ CH3), 3.22 (sept, 3J ¼ 6.8 Hz, 1H, tert. isopropyl-
H), 5.22 (dd, 3J ¼ 11.0 Hz, 2J ¼ 1.8 Hz, 1H,
b-H trans to aryl), 5.50 (dd,
3J ¼ 17.5 Hz, 2J ¼ 1.8 Hz, 1H,
b
-H cis), 7.03 (dd, 3J ¼ 17.5 and 11.0 Hz,
1H,
a
-H), ca. 7.13 (broad m, 4H, C6H4) ppm; 1H NMR ([D8]THF,
60 MHz)
values, assigned as described in the Main Text; 13C NMR ([D8]THF,
22.63 MHz) ),
23.7 (q, 2 ꢄ CH3), 29.7 (d, tert. CH), 115.6 (t, CH2-
125.3 (d, C-5), 126.4 (d, C-3), 126.7 (d, C-6), 128.6 (d, C-4), 135.8
(quat, C- ), 136.8 (quat, C-1), 146.2 (quat, C-2) ppm, assigned
through the off-resonance multiplet patterns and as described in
d 1.20, 3.25, 5.23, 5.53, 7.10, 7.15 ppm with unchanged J
d
b
a
the Main Text; IR (film)
n 3080, 3057, 3020, 2960 (s), 2865, 1622
(C]C), 1480, 1446, 986, 908, 752 (s) cmꢀ1; UV/VIS (cyclohexane)
lmax (log ε) 207 (4.43), 243 (4.05), 286 (2.81), 297 (2.53) nm. Anal.
calcd for C11H14 (146.2): C, 90.35; H, 9.65. Found: C, 90.59; H, 9.64.
(81%), bp 101e101.5 ꢁC/12 Torr; 1H NMR (CDCl3, 60 MHz)
d 1.22 (d,
3J ¼ 7.0 Hz, ca. 6H, 2 ꢄ CH3), 3.33 (sept, 3J ¼ 7.0 Hz, 1H, tert.