Stereoselective Radical Aryl Migration from Si to C
J . Org. Chem., Vol. 65, No. 14, 2000 4287
Elemental analyses were performed by the Microanalytical
Laboratory of the Laboratorium fu¨r Organische Chemie, ETH-
Zu¨rich.
7.02 (m, 13H), 2.95 (q, 4H, J ) 13.6 Hz), 0.93 (t, 6H, J ) 13.6
Hz), 0.43 (s, 6H). Bis(4-fluorophenyl)(N,N-diethylamino)(di-
methylphenylsilyl)silane (3.20 g, 7.5 mmol) was dissolved in
CH2Cl2 (7 mL) at 0 °C, and acetyl chloride (0.54 mL, 7.5 mmol)
was added.47 After 2 h, the solvent was removed and the
residue distilled (0.02 Torr, 100-120 °C) to afford 35: 2.39 g
Gen er a l P r oced u r e (GP 1) for th e Silyla tion of Sec-
on d a r y Alcoh ols. The chlorosilane was dissolved under Ar
in Et2O, THF, or CH2Cl2. The solution was cooled to 0 °C, and
NEt3 was added. A solution of the alcohol in Et2O, THF, or
CH2Cl2 was added over 3 min. DMAP was added, and the
suspension formed was allowed to warm to rt and stirred for
3-12 h. Addition of hexane or pentane and filtration of the
solid gave after evaporation of the solvent the crude product
which was purified either by distillation or flash chromatog-
raphy.
Gen er a l P r oced u r e (GP 2) for t h e Ar yl Migr a t ion
Rea ction . The silyl ether was dissolved in benzene under
argon and heated to reflux followed by slow addition of Bu3-
SnH and AIBN in benzene over 7 h. After complete addition
of the tin hydride solution, stirring was continued at that
temperature for 30 min. The solution was then allowed to
warm to rt, and MeLi was added. This was followed by stirring
at rt for 12 h and then slow addition of H2O and Et2O. The
reaction mixture was washed with saturated aqueous NH4Cl
and brine. The organic phase was dried (MgSO4) and evapo-
rated to yield the crude product.
1
(82%) in about 90% purity. H NMR (300 MHz, CDCl3) 7.47-
7.02 (m, 13H), 0.53 (s, 6H). 13C NMR (75 MHz, CDCl3) 164.7
(d, J C-F ) 251.4 Hz), 136.9 (d, J C-F ) 7.3 Hz), 134.5, 129.7,
128.3, 116.2, 115.7 (d, J C-F ) 19.5 Hz), -4.0.
Rep r esen ta tive Exa m p le for th e Syn th esis of Silyl
Eth er s Bear in g Fu n ction alized P h en yl Gr ou ps: l-[(4-Iodo-
p en ta n -2-oxy)bis(4-flu or op h en yl)silyl]d im eth ylp h en yl-
sila n e (39). According to GP 1 with 35 (445 mg, 1.1 mmol),
THF (6 mL + 2 mL), l-4-iodopentan-2-ol (237 mg, 1.10 mmol),
NEt3 (0.15 mL, 1.10 mmol), and DMAP (cat.), and a reaction
time of 4 h at 0 °C. Purification by FC (Et2O/pentane 1:200)
afforded 39: 180 mg (29%). IR (CHCl3) 2964 w, 1587 s, 1498
s, 1160 m, 1054 m cm-1 1H NMR (400 MHz, CDCl3) 7.51-
.
7.43 (m, 4H), 7.37-7.25 (m, 5H), 7.07-7.02 (m, 4H), 4.18-
4.10 (m, 1H), 4.00-3.93 (m, 1H), 1.92-1.81 (m, 1H), 1.85 (d,
3H, J ) 6.9 Hz), 1.65-1.58 (m, 1H), 1.02 (d, 3H, J ) 6.1 Hz),
0.48 (s, 3H), 0.46 (s, 3H). 13C NMR (100 MHz, CDCl3) 164.1
(d, J C-F ) 249.4 Hz), 164.0 (d, J C-F ) 249.0 Hz), 137.7, 137.2
(d, J C-F ) 7.6 Hz), 136.9 (d, J C-F ) 7.5 Hz), 134.3, 132.3 (d,
J C-F ) 3.8 Hz), 131.7 (d, J C-F ) 3.8 Hz), 128.9, 127.8, 115.1
(d, J C-F ) 19.8 Hz), 115.1 (d, J C-F ) 19.8 Hz), 70.8, 52.7, 29.5,
27.5, 24.0, -2.7, -2.8. MS (EI) 431.1 (14, [M - Si(CH3)2-
(C6H5)]+), 345.0 (100). HRMS calcd for ([M - Si(CH3)2Ph]+)
Rep r esen ta tive Exa m p le for th e Syn th esis of Silyl
Eth er s Bea r in g Un fu n ction a lized P h en yl Gr ou p s: l-[(4-
Iod op en ta n -2-oxy)d ip h en ylsilyl]tr im eth ylsila n e (5). Ac-
cording to GP 1 with 1-chloro-2,2,2-trimethyl-1,1-diphenyl-
disilane28 (870 mg, 3.0 mmol), THF (13 mL + 3 mL), l-4-
iodopentan-2-ol (700 mg, 3.30 mmol), NEt3 (0.49 mL, 3.35
mmol), and DMAP (cat.), and a reaction time of 12 h at rt.
Purification by FC (Et2O/pentane 1:100) afforded 5: 1.13 g
(80%). IR (CHCl3) 3068 s, 2966 s, 1958 w, 1888w, 1824 w, 1774
C
17H18F2IOSi: 431.0140; found: 431.0143.
Rep r esen ta tive Exa m p le of a 1,5 Ar yl Migr a tion w ith
F u n ction a lized P h en yl Gr ou p s: l-4-(4-F lu or op h en yl)-
p en ta n -2-ol (42). According to GP 2 with silyl ether 39 (208
mg, 0.36 mmol), benzene (7 mL), Bu3SnH (103 µL, 0.39 mmol),
AIBN (7 mg, 0.04 mmol) in benzene (0.9 mL), and MeLi (3.4
mL, 5.44 mmol). Purification by FC (Et2O/pentane 1:6) afforded
42: 24 mg (36%). The diastereoisomer ratio (u:l ) 10:1) was
determined by GC-analysis. IR (CHCl3) 3609 m, 2967 s, 1604
1
w, 1428 s, 1144 s, 1106 s, 1056 s cm-1; H NMR (400 MHz)
7.64-7.54 (m, 4H), 7.42-7.34 (m, 6H), 4.35-4.26 (m, 1H),
4.08-4.00 (m, 1H), 1.95-1.87 (m, 1H), 1.89 (d, 3H, J ) 6.9
Hz), 1.73-1.66 (m, 1H), 1.14 (d, 3H, J ) 6.1 Hz), 0.21 (d, 9H,
J ) 0.4 Hz); 13C NMR (100 MHz) 137.3, 137.1, 135.0, 134.8,
129.5, 129.4, 127.8, 127.7, 70.5, 52.9, 29.6, 27.7, 24.1, -1.0;
MS (EI) 469.1 (<1, [M + H]+), 453.1 (<1, [M - CH3]+), 309.0
(100). Anal. Calcd for C20H29IOSi2 (468.52): C, 51.27; H, 6.24.
Found: C, 51.40; H 6.35.
1
m, 1509 s, 1158 m, 1093 m cm-1. H NMR (400 MHz) 7.19-
7.13 (m, 2H), 7.01-6.95 (m, 2H), 3.79-3.71 (m, 1H), 2.87 (qt,
1H, J 1 ) J 2 ) 7.1 Hz), 1.82-1.74 (m, 1H), 1.65-1.58 (m, 1H),
1.24 (d, 3H, J ) 6.9 Hz), 1.19 (d, 3H, J ) 6.2 Hz). 13C NMR
(100 MHz) 161.3 (d, J CF ) 243.8 Hz), 143.0 (d, J CF ) 3.0 Hz),
128.1 (d, J CF ) 7.7 Hz), 115.2 (d, J CF ) 20.9 Hz), 66.3, 47.9,
36.1, 23.8, 22.4. MS (EI) 182.2 (3, [M]+), 123.2 (100). HRMS
calcd for ([M]+) C11H15FO: 182.1103; found: 182.1106.
Rep r esen ta tive Exa m p le of a 1,5 P h en yl Migr a tion :
4-P h en ylp en ta n -2-ol (3). According to GP 2 with silyl ether
5 (114 mg, 0.24 mmol), benzene (5 mL), Bu3SnH (65 µL, 0.24
mmol), AIBN (8 mg, 0.04 mmol) in benzene (0.5 mL), and MeLi
(2.3 mL, 3.7 mmol). Purification by FC (Et2O/pentane 1:4)
afforded 3: 28 mg (70%). The physical data are in agreement
with the values reported in the literature.26 The diastereoiso-
mer ratio (u:l ) 10:1) was determined by GC-analysis.
Rep r esen ta tive Exa m p le for th e Syn th esis of th e
Ch lor osila n es Bea r in g F u n ction a lized P h en yl Gr ou p s:
1-Ch lor o-2,2-d im eth yl-1,1-bis(4-flu or op h en yl)-2-p h en yl-
d isila n e (35). Bis(4-fluorophenyl)dichlorosilane (18.8 g, 65
mmol) was dissolved under Ar in THF (48 mL) and cooled to
0 °C. NEt3 (10.4 mL, 75 mmol) and HNEt2 (6.75 mL, 65 mmol)
were added according to a literature procedure.45 After stirring
for 4 h at 0 °C, hexane was added, and the suspension was
filtered and distilled (0.01 Torr, 80-95 °C) to afford (chlorobis-
(4-fluorophenyl)silanyl)diethylamide (17.9 g, 84%). 1H NMR
(200 MHz, CDCl3) 7.79-7.68 (m, 4H), 7.22-7.06 (m, 4H), 2.93
(q, 4H, J ) 7.1 Hz), 1.06 (t, 6H, J ) 7.1 Hz). Dimethylphen-
ylchlorosilane (2.9 mL, 17.5 mmol) and Li-wire (0.43 g, 62
mmol) were reacted in THF (35 mL) at 0 °C according to ref
28. The Li-silanide solution formed was slowly added to a
solution of (chlorobis(4-fluorophenyl)silanyl)diethylamide (5.70
g, 17.5 mmol) in THF (13 mL) at 0 °C.46 After stirring for 1 h
at 0 °C, hexane (90 mL) was added, and the salts were filtered
off under Ar. Distillation (0.02 Torr, 115-135 °C afforded
bis(4-flu or oph en yl)(N,N-diet h yla m in o)(dim et h ylph en yl-
silyl)silane (3.20 g, 43%). 1H NMR (200 MHz, CDCl3) 7.48-
Rep r esen ta tive Exa m p le for th e Syn th esis of th e Silyl
Eth er s for th e 1,4 Ar yl Migr a tion : [(3-Br om obu ta n -2-
oxy)d ip h en ylsilyl]tr im eth ylsila n e (45). According to GP 1
with 1-chloro-2,2,2-trimethyl-1,1-diphenyldisilane28 (156 mg,
0.52 mmol), Et2O (5 mL + 2 mL), 3-bromobutan-2-ol (79 mg,
0.52 mmol), NEt3 (0.08 mL, 0.52 mmol), and DMAP (cat.), and
a reaction time of 12 h at rt. Purification by FC (Et 2O/pentane
1:100) afforded 45: 100 mg (47%). IR (CHCl3) 2955 m, 1588
w, 1428 s, 1107 s, 856 s cm-1 1H NMR (400 MHz, CDCl3)
.
isomer A: 7.65-7.49 (m, 4H), 7.47-7.28 (m, 6H), 4.06-3.97
(m, 1H), 3.90-3.84 (m, 1H), 1.60 (d, 3H, J ) 6.8 Hz), 1.19 (d,
3H, J ) 6.1 Hz), 0.20 (s, 9H). Isomer B: 7.65-7.49 (m, 4H),
7.47-7.28 (m, 6H), 4.06-3.97 (m, 1H), 3.90-3.84 (m, 1H), 1.63
(d, 3H, J ) 6.7 Hz), 1.21 (d, 3H, J ) 6.3 Hz), 0.20 (s, 9H). 13C
NMR (100 MHz, CDCl3) isomer A: 136.8, 136.6, 135.0, 134.8,
129.6, 129.5, 127.9, 127.8, 73.7, 56.2, 21.5, 20.7, -1.3. Isomer
B: 136.8, 136.6, 134.8, 134.7, 129.6, 129.6, 127.9, 127.8, 72.9,
54.0, 19.9, 18.9, -1.3. MS (EI) 333.1 (36, [M - Si(CH3)3]+),
261.0 (100). HRMS calcd for ([M - Si(CH3)3]+) C16H18 79BrO-
Si: 333.0310; found: 333.0303.
Rep r esen ta tive Exa m p le for th e Syn th esis of th e
Silyla ted Ester s: 3-(Dip h en yl(tr im eth ylsilyl)silyloxy)-2-
(p h en ylsela n yl)bu tyr ic Acid ter t-Bu tyl Ester (47). Ac-
cording to GP 1 with 1-chloro-2,2,2-trimethyl-1,1-diphenyl-
disilane28 (222 mg, 0.76 mmol), THF (4 mL + 2 mL), 3-hydroxy-
(45) Tamao, K.; Nakajo, E.; Ito, Y. Tetrahedron 1988, 44, 3997.
(46) Murakami, M.; Suginome, M.; Fujimoto, K.; Nakamura, H.;
Andersson, P. G.; Ito, Y. J . Am. Chem. Soc. 1993, 115, 6487.
(47) Kawachi, A.; Doi, N.; Tamao, K. J . Am. Chem. Soc. 1997, 119,
233. See also refs 28. and 46.